Merge pull request #1985 from usamoi/vpmaddwd

sayantn · web-flow · commit 85f3ba3dd1d4 · 2026-01-02T19:35:29.000Z
Use LLVM intrinsics for `madd` intrinsics
diff --git a/library/stdarch/crates/core_arch/src/x86/avx2.rs b/library/stdarch/crates/core_arch/src/x86/avx2.rs
@@ -1813,14 +1813,20 @@ pub const fn _mm256_inserti128_si256<const IMM1: i32>(a: __m256i, b: __m128i) ->
 #[target_feature(enable = "avx2")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
 #[stable(feature = "simd_x86", since = "1.27.0")]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm256_madd_epi16(a: __m256i, b: __m256i) -> __m256i {
-    unsafe {
-        let r: i32x16 = simd_mul(simd_cast(a.as_i16x16()), simd_cast(b.as_i16x16()));
-        let even: i32x8 = simd_shuffle!(r, r, [0, 2, 4, 6, 8, 10, 12, 14]);
-        let odd: i32x8 = simd_shuffle!(r, r, [1, 3, 5, 7, 9, 11, 13, 15]);
-        simd_add(even, odd).as_m256i()
-    }
+pub fn _mm256_madd_epi16(a: __m256i, b: __m256i) -> __m256i {
+    // It's a trick used in the Adler-32 algorithm to perform a widening addition.
+    //
+    // ```rust
+    // #[target_feature(enable = "avx2")]
+    // unsafe fn widening_add(mad: __m256i) -> __m256i {
+    //     _mm256_madd_epi16(mad, _mm256_set1_epi16(1))
+    // }
+    // ```
+    //
+    // If we implement this using generic vector intrinsics, the optimizer
+    // will eliminate this pattern, and `vpmaddwd` will no longer be emitted.
+    // For this reason, we use x86 intrinsics.
+    unsafe { transmute(pmaddwd(a.as_i16x16(), b.as_i16x16())) }
 }
 
 /// Vertically multiplies each unsigned 8-bit integer from `a` with the
@@ -3789,6 +3795,8 @@ unsafe extern "C" {
     fn phaddsw(a: i16x16, b: i16x16) -> i16x16;
     #[link_name = "llvm.x86.avx2.phsub.sw"]
     fn phsubsw(a: i16x16, b: i16x16) -> i16x16;
+    #[link_name = "llvm.x86.avx2.pmadd.wd"]
+    fn pmaddwd(a: i16x16, b: i16x16) -> i32x8;
     #[link_name = "llvm.x86.avx2.pmadd.ub.sw"]
     fn pmaddubsw(a: u8x32, b: i8x32) -> i16x16;
     #[link_name = "llvm.x86.avx2.mpsadbw"]
@@ -4637,7 +4645,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx2")]
-    const fn test_mm256_madd_epi16() {
+    fn test_mm256_madd_epi16() {
         let a = _mm256_set1_epi16(2);
         let b = _mm256_set1_epi16(4);
         let r = _mm256_madd_epi16(a, b);
diff --git a/library/stdarch/crates/core_arch/src/x86/avx512bw.rs b/library/stdarch/crates/core_arch/src/x86/avx512bw.rs
@@ -6321,22 +6321,20 @@ pub const unsafe fn _mm_mask_storeu_epi8(mem_addr: *mut i8, mask: __mmask16, a:
 #[target_feature(enable = "avx512bw")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm512_madd_epi16(a: __m512i, b: __m512i) -> __m512i {
-    unsafe {
-        let r: i32x32 = simd_mul(simd_cast(a.as_i16x32()), simd_cast(b.as_i16x32()));
-        let even: i32x16 = simd_shuffle!(
-            r,
-            r,
-            [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30]
-        );
-        let odd: i32x16 = simd_shuffle!(
-            r,
-            r,
-            [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31]
-        );
-        simd_add(even, odd).as_m512i()
-    }
+pub fn _mm512_madd_epi16(a: __m512i, b: __m512i) -> __m512i {
+    // It's a trick used in the Adler-32 algorithm to perform a widening addition.
+    //
+    // ```rust
+    // #[target_feature(enable = "avx512bw")]
+    // unsafe fn widening_add(mad: __m512i) -> __m512i {
+    //     _mm512_madd_epi16(mad, _mm512_set1_epi16(1))
+    // }
+    // ```
+    //
+    // If we implement this using generic vector intrinsics, the optimizer
+    // will eliminate this pattern, and `vpmaddwd` will no longer be emitted.
+    // For this reason, we use x86 intrinsics.
+    unsafe { transmute(vpmaddwd(a.as_i16x32(), b.as_i16x32())) }
 }
 
 /// Multiply packed signed 16-bit integers in a and b, producing intermediate signed 32-bit integers. Horizontally add adjacent pairs of intermediate 32-bit integers, and pack the results in dst using writemask k (elements are copied from src when the corresponding mask bit is not set).
@@ -6346,8 +6344,7 @@ pub const fn _mm512_madd_epi16(a: __m512i, b: __m512i) -> __m512i {
 #[target_feature(enable = "avx512bw")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm512_mask_madd_epi16(src: __m512i, k: __mmask16, a: __m512i, b: __m512i) -> __m512i {
+pub fn _mm512_mask_madd_epi16(src: __m512i, k: __mmask16, a: __m512i, b: __m512i) -> __m512i {
     unsafe {
         let madd = _mm512_madd_epi16(a, b).as_i32x16();
         transmute(simd_select_bitmask(k, madd, src.as_i32x16()))
@@ -6361,8 +6358,7 @@ pub const fn _mm512_mask_madd_epi16(src: __m512i, k: __mmask16, a: __m512i, b: _
 #[target_feature(enable = "avx512bw")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm512_maskz_madd_epi16(k: __mmask16, a: __m512i, b: __m512i) -> __m512i {
+pub fn _mm512_maskz_madd_epi16(k: __mmask16, a: __m512i, b: __m512i) -> __m512i {
     unsafe {
         let madd = _mm512_madd_epi16(a, b).as_i32x16();
         transmute(simd_select_bitmask(k, madd, i32x16::ZERO))
@@ -6376,8 +6372,7 @@ pub const fn _mm512_maskz_madd_epi16(k: __mmask16, a: __m512i, b: __m512i) -> __
 #[target_feature(enable = "avx512bw,avx512vl")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm256_mask_madd_epi16(src: __m256i, k: __mmask8, a: __m256i, b: __m256i) -> __m256i {
+pub fn _mm256_mask_madd_epi16(src: __m256i, k: __mmask8, a: __m256i, b: __m256i) -> __m256i {
     unsafe {
         let madd = _mm256_madd_epi16(a, b).as_i32x8();
         transmute(simd_select_bitmask(k, madd, src.as_i32x8()))
@@ -6391,8 +6386,7 @@ pub const fn _mm256_mask_madd_epi16(src: __m256i, k: __mmask8, a: __m256i, b: __
 #[target_feature(enable = "avx512bw,avx512vl")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm256_maskz_madd_epi16(k: __mmask8, a: __m256i, b: __m256i) -> __m256i {
+pub fn _mm256_maskz_madd_epi16(k: __mmask8, a: __m256i, b: __m256i) -> __m256i {
     unsafe {
         let madd = _mm256_madd_epi16(a, b).as_i32x8();
         transmute(simd_select_bitmask(k, madd, i32x8::ZERO))
@@ -6406,8 +6400,7 @@ pub const fn _mm256_maskz_madd_epi16(k: __mmask8, a: __m256i, b: __m256i) -> __m
 #[target_feature(enable = "avx512bw,avx512vl")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm_mask_madd_epi16(src: __m128i, k: __mmask8, a: __m128i, b: __m128i) -> __m128i {
+pub fn _mm_mask_madd_epi16(src: __m128i, k: __mmask8, a: __m128i, b: __m128i) -> __m128i {
     unsafe {
         let madd = _mm_madd_epi16(a, b).as_i32x4();
         transmute(simd_select_bitmask(k, madd, src.as_i32x4()))
@@ -6421,8 +6414,7 @@ pub const fn _mm_mask_madd_epi16(src: __m128i, k: __mmask8, a: __m128i, b: __m12
 #[target_feature(enable = "avx512bw,avx512vl")]
 #[stable(feature = "stdarch_x86_avx512", since = "1.89")]
 #[cfg_attr(test, assert_instr(vpmaddwd))]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm_maskz_madd_epi16(k: __mmask8, a: __m128i, b: __m128i) -> __m128i {
+pub fn _mm_maskz_madd_epi16(k: __mmask8, a: __m128i, b: __m128i) -> __m128i {
     unsafe {
         let madd = _mm_madd_epi16(a, b).as_i32x4();
         transmute(simd_select_bitmask(k, madd, i32x4::ZERO))
@@ -12582,6 +12574,8 @@ unsafe extern "C" {
     #[link_name = "llvm.x86.avx512.pmul.hr.sw.512"]
     fn vpmulhrsw(a: i16x32, b: i16x32) -> i16x32;
 
+    #[link_name = "llvm.x86.avx512.pmaddw.d.512"]
+    fn vpmaddwd(a: i16x32, b: i16x32) -> i32x16;
     #[link_name = "llvm.x86.avx512.pmaddubs.w.512"]
     fn vpmaddubsw(a: u8x64, b: i8x64) -> i16x32;
 
@@ -17486,7 +17480,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw")]
-    const fn test_mm512_madd_epi16() {
+    fn test_mm512_madd_epi16() {
         let a = _mm512_set1_epi16(1);
         let b = _mm512_set1_epi16(1);
         let r = _mm512_madd_epi16(a, b);
@@ -17495,7 +17489,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw")]
-    const fn test_mm512_mask_madd_epi16() {
+    fn test_mm512_mask_madd_epi16() {
         let a = _mm512_set1_epi16(1);
         let b = _mm512_set1_epi16(1);
         let r = _mm512_mask_madd_epi16(a, 0, a, b);
@@ -17523,7 +17517,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw")]
-    const fn test_mm512_maskz_madd_epi16() {
+    fn test_mm512_maskz_madd_epi16() {
         let a = _mm512_set1_epi16(1);
         let b = _mm512_set1_epi16(1);
         let r = _mm512_maskz_madd_epi16(0, a, b);
@@ -17534,7 +17528,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw,avx512vl")]
-    const fn test_mm256_mask_madd_epi16() {
+    fn test_mm256_mask_madd_epi16() {
         let a = _mm256_set1_epi16(1);
         let b = _mm256_set1_epi16(1);
         let r = _mm256_mask_madd_epi16(a, 0, a, b);
@@ -17554,7 +17548,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw,avx512vl")]
-    const fn test_mm256_maskz_madd_epi16() {
+    fn test_mm256_maskz_madd_epi16() {
         let a = _mm256_set1_epi16(1);
         let b = _mm256_set1_epi16(1);
         let r = _mm256_maskz_madd_epi16(0, a, b);
@@ -17565,7 +17559,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw,avx512vl")]
-    const fn test_mm_mask_madd_epi16() {
+    fn test_mm_mask_madd_epi16() {
         let a = _mm_set1_epi16(1);
         let b = _mm_set1_epi16(1);
         let r = _mm_mask_madd_epi16(a, 0, a, b);
@@ -17576,7 +17570,7 @@ mod tests {
     }
 
     #[simd_test(enable = "avx512bw,avx512vl")]
-    const fn test_mm_maskz_madd_epi16() {
+    fn test_mm_maskz_madd_epi16() {
         let a = _mm_set1_epi16(1);
         let b = _mm_set1_epi16(1);
         let r = _mm_maskz_madd_epi16(0, a, b);
diff --git a/library/stdarch/crates/core_arch/src/x86/sse2.rs b/library/stdarch/crates/core_arch/src/x86/sse2.rs
@@ -210,14 +210,20 @@ pub const fn _mm_avg_epu16(a: __m128i, b: __m128i) -> __m128i {
 #[target_feature(enable = "sse2")]
 #[cfg_attr(test, assert_instr(pmaddwd))]
 #[stable(feature = "simd_x86", since = "1.27.0")]
-#[rustc_const_unstable(feature = "stdarch_const_x86", issue = "149298")]
-pub const fn _mm_madd_epi16(a: __m128i, b: __m128i) -> __m128i {
-    unsafe {
-        let r: i32x8 = simd_mul(simd_cast(a.as_i16x8()), simd_cast(b.as_i16x8()));
-        let even: i32x4 = simd_shuffle!(r, r, [0, 2, 4, 6]);
-        let odd: i32x4 = simd_shuffle!(r, r, [1, 3, 5, 7]);
-        simd_add(even, odd).as_m128i()
-    }
+pub fn _mm_madd_epi16(a: __m128i, b: __m128i) -> __m128i {
+    // It's a trick used in the Adler-32 algorithm to perform a widening addition.
+    //
+    // ```rust
+    // #[target_feature(enable = "sse2")]
+    // unsafe fn widening_add(mad: __m128i) -> __m128i {
+    //     _mm_madd_epi16(mad, _mm_set1_epi16(1))
+    // }
+    // ```
+    //
+    // If we implement this using generic vector intrinsics, the optimizer
+    // will eliminate this pattern, and `pmaddwd` will no longer be emitted.
+    // For this reason, we use x86 intrinsics.
+    unsafe { transmute(pmaddwd(a.as_i16x8(), b.as_i16x8())) }
 }
 
 /// Compares packed 16-bit integers in `a` and `b`, and returns the packed
@@ -3187,6 +3193,8 @@ unsafe extern "C" {
     fn lfence();
     #[link_name = "llvm.x86.sse2.mfence"]
     fn mfence();
+    #[link_name = "llvm.x86.sse2.pmadd.wd"]
+    fn pmaddwd(a: i16x8, b: i16x8) -> i32x4;
     #[link_name = "llvm.x86.sse2.psad.bw"]
     fn psadbw(a: u8x16, b: u8x16) -> u64x2;
     #[link_name = "llvm.x86.sse2.psll.w"]
@@ -3467,7 +3475,7 @@ mod tests {
     }
 
     #[simd_test(enable = "sse2")]
-    const fn test_mm_madd_epi16() {
+    fn test_mm_madd_epi16() {
         let a = _mm_setr_epi16(1, 2, 3, 4, 5, 6, 7, 8);
         let b = _mm_setr_epi16(9, 10, 11, 12, 13, 14, 15, 16);
         let r = _mm_madd_epi16(a, b);
