[llvm] [InstCombine] Removing the combine of fmuladd with fast flag (PR #90434)

[via llvm-commits]

https://github.com/vfdff updated https://github.com/llvm/llvm-project/pull/90434

>From 2631531764f0e732a0e96ab066de27d08b604655 Mon Sep 17 00:00:00 2001
From: zhongyunde 00443407 <zhongyunde at huawei.com>
Date: Sun, 28 Apr 2024 20:48:32 -0400
Subject: [PATCH 1/2] [InstCombine] Removing the combine of fmuladd with fast
 flag

We should treat fmuladd like an fma intrinsic, and any regressions need to be
addressed by dealing with fma/fmuladd in other contexts.
---
 .../lib/Transforms/InstCombine/InstCombineCalls.cpp | 11 -----------
 llvm/test/Transforms/InstCombine/fma.ll             | 13 +++++--------
 2 files changed, 5 insertions(+), 19 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index cdec8c8c7c807..b6f339da31f7f 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -2424,17 +2424,6 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     break;
   }
   case Intrinsic::fmuladd: {
-    // Canonicalize fast fmuladd to the separate fmul + fadd.
-    if (II->isFast()) {
-      BuilderTy::FastMathFlagGuard Guard(Builder);
-      Builder.setFastMathFlags(II->getFastMathFlags());
-      Value *Mul = Builder.CreateFMul(II->getArgOperand(0),
-                                      II->getArgOperand(1));
-      Value *Add = Builder.CreateFAdd(Mul, II->getArgOperand(2));
-      Add->takeName(II);
-      return replaceInstUsesWith(*II, Add);
-    }
-
     // Try to simplify the underlying FMul.
     if (Value *V = simplifyFMulInst(II->getArgOperand(0), II->getArgOperand(1),
                                     II->getFastMathFlags(),
diff --git a/llvm/test/Transforms/InstCombine/fma.ll b/llvm/test/Transforms/InstCombine/fma.ll
index cf3d7f3c525a5..cf58cebb6978a 100644
--- a/llvm/test/Transforms/InstCombine/fma.ll
+++ b/llvm/test/Transforms/InstCombine/fma.ll
@@ -194,8 +194,7 @@ define float @fmuladd_unary_fneg_x_unary_fneg_y(float %x, float %y, float %z) {
 
 define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_fneg_x_fneg_y_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fneg = fsub float -0.0, %x
@@ -206,8 +205,7 @@ define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
 
 define float @fmuladd_unary_fneg_x_unary_fneg_y_fast(float %x, float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_unary_fneg_x_unary_fneg_y_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[Y:%.*]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fneg = fneg float %x
@@ -285,8 +283,7 @@ define float @fmuladd_fabs_x_fabs_x(float %x, float %z) {
 
 define float @fmuladd_fabs_x_fabs_x_fast(float %x, float %z) {
 ; CHECK-LABEL: @fmuladd_fabs_x_fabs_x_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[X:%.*]], [[X]]
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[X]], float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %x.fabs = call float @llvm.fabs.f32(float %x)
@@ -312,10 +309,10 @@ define float @fma_k_y_z_fast(float %y, float %z) {
   ret float %fma
 }
 
+; Treat fmuladd like an fma intrinsic
 define float @fmuladd_k_y_z_fast(float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_k_y_z_fast(
-; CHECK-NEXT:    [[TMP1:%.*]] = fmul fast float [[Y:%.*]], 4.000000e+00
-; CHECK-NEXT:    [[FMULADD:%.*]] = fadd fast float [[TMP1]], [[Z:%.*]]
+; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[Y:%.*]], float 4.000000e+00, float [[Z:%.*]])
 ; CHECK-NEXT:    ret float [[FMULADD]]
 ;
   %fmuladd = call fast float @llvm.fmuladd.f32(float 4.0, float %y, float %z)

>From f2e787e7030126f5f55bb4e90cc83827f25e1219 Mon Sep 17 00:00:00 2001
From: zhongyunde 00443407 <zhongyunde at huawei.com>
Date: Sun, 28 Apr 2024 20:48:32 -0400
Subject: [PATCH 2/2] [InstCombine] Add some tests with reduced flag sets, NFC

We remove the combine for fmuladd with fast flag on PR90434,
and add these tests with reduced flags to show they have identity
results.
---
 llvm/test/Transforms/InstCombine/fma.ll | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/fma.ll b/llvm/test/Transforms/InstCombine/fma.ll
index cf58cebb6978a..b88250d434280 100644
--- a/llvm/test/Transforms/InstCombine/fma.ll
+++ b/llvm/test/Transforms/InstCombine/fma.ll
@@ -203,6 +203,24 @@ define float @fmuladd_fneg_x_fneg_y_fast(float %x, float %y, float %z) {
   ret float %fmuladd
 }
 
+define float @fmuladd_unfold(float %x, float %y, float %z) {
+; CHECK-LABEL: @fmuladd_unfold(
+; CHECK-NEXT:    [[FMULADD:%.*]] = call reassoc contract float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])
+; CHECK-NEXT:    ret float [[FMULADD]]
+;
+  %fmuladd = call reassoc contract float @llvm.fmuladd.f32(float %x, float %y, float %z)
+  ret float %fmuladd
+}
+
+define <8 x half> @fmuladd_unfold_vec(<8 x half> %x, <8 x half> %y, <8 x half> %z) {
+; CHECK-LABEL: @fmuladd_unfold_vec(
+; CHECK-NEXT:    [[FMULADD:%.*]] = call reassoc contract <8 x half> @llvm.fmuladd.v8f16(<8 x half> [[X:%.*]], <8 x half> [[Y:%.*]], <8 x half> [[Z:%.*]])
+; CHECK-NEXT:    ret <8 x half> [[FMULADD]]
+;
+  %fmuladd = call reassoc contract <8 x half> @llvm.fmuladd.v8f16(<8 x half> %x, <8 x half> %y, <8 x half> %z)
+  ret <8 x half> %fmuladd
+}
+
 define float @fmuladd_unary_fneg_x_unary_fneg_y_fast(float %x, float %y, float %z) {
 ; CHECK-LABEL: @fmuladd_unary_fneg_x_unary_fneg_y_fast(
 ; CHECK-NEXT:    [[FMULADD:%.*]] = call fast float @llvm.fmuladd.f32(float [[X:%.*]], float [[Y:%.*]], float [[Z:%.*]])