[PATCH] D32301: Don't pass FPOpFusion::Strict to the backend

[Adam Nemet via Phabricator via cfe-commits]

anemet created this revision.

This restores the behavior prior to https://reviews.llvm.org/D31167 where the 
code-gen default was
FPC_On which mapped to FPOpFusion::Standard.  After merging the FE
state (on/off) and the code-gen state (on/fast/off), the default became off to
match the front-end.

In other words, the front-end controls when to fuse along the language
standards and the backend shouldn't override this by splitting fused
intrinsics as FPOpFusion::Strict would imply.


https://reviews.llvm.org/D32301

Files:
  lib/CodeGen/BackendUtil.cpp
  test/CodeGen/fp-contract-on-asm.c


Index: test/CodeGen/fp-contract-on-asm.c
===================================================================
--- /dev/null
+++ test/CodeGen/fp-contract-on-asm.c
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -O3 -triple=aarch64-apple-ios -S -o - %s | FileCheck %s
+// REQUIRES: aarch64-registered-target
+
+float fma_test1(float a, float b, float c) {
+#pragma STDC FP_CONTRACT ON
+// CHECK-LABEL: fma_test1:
+// CHECK: fmadd
+  float x = a * b + c;
+  return x;
+}
+
+float fma_test2(float a, float b, float c) {
+// CHECK-LABEL: fma_test2:
+// CHECK: fmul
+// CHECK: fadd
+  float x = a * b + c;
+  return x;
+}
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -372,7 +372,9 @@
   // Set FP fusion mode.
   switch (LangOpts.getDefaultFPContractMode()) {
   case LangOptions::FPC_Off:
-    Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
+    // Preserve any contraction performed by the front-end.  (Strict performs
+    // splitting of the muladd instrinsic in the backend.)
+    Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
     break;
   case LangOptions::FPC_On:
     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;



Index: test/CodeGen/fp-contract-on-asm.c
===================================================================
--- /dev/null
+++ test/CodeGen/fp-contract-on-asm.c
@@ -0,0 +1,18 @@
+// RUN: %clang_cc1 -O3 -triple=aarch64-apple-ios -S -o - %s | FileCheck %s
+// REQUIRES: aarch64-registered-target
+
+float fma_test1(float a, float b, float c) {
+#pragma STDC FP_CONTRACT ON
+// CHECK-LABEL: fma_test1:
+// CHECK: fmadd
+  float x = a * b + c;
+  return x;
+}
+
+float fma_test2(float a, float b, float c) {
+// CHECK-LABEL: fma_test2:
+// CHECK: fmul
+// CHECK: fadd
+  float x = a * b + c;
+  return x;
+}
Index: lib/CodeGen/BackendUtil.cpp
===================================================================
--- lib/CodeGen/BackendUtil.cpp
+++ lib/CodeGen/BackendUtil.cpp
@@ -372,7 +372,9 @@
   // Set FP fusion mode.
   switch (LangOpts.getDefaultFPContractMode()) {
   case LangOptions::FPC_Off:
-    Options.AllowFPOpFusion = llvm::FPOpFusion::Strict;
+    // Preserve any contraction performed by the front-end.  (Strict performs
+    // splitting of the muladd instrinsic in the backend.)
+    Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;
     break;
   case LangOptions::FPC_On:
     Options.AllowFPOpFusion = llvm::FPOpFusion::Standard;

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