[PATCH] D76949: Replace subtract-from-zero float in version with fneg in PowerPC special fma compiler builtins

[Andrew J Wock via Phabricator via cfe-commits]

ajwock created this revision.
ajwock added reviewers: kpn, cameron.mcinally, spatel, hfinkel.
Herald added subscribers: cfe-commits, steven.zhang, shchenz, kbarton, nemanjai.
Herald added a project: clang.
ajwock added a reviewer: nemanjai.
Herald added a subscriber: wuzish.

This patch adds a test for the PowerPC fma compiler builtins, some variations of which negate inputs and outputs.  The code to generate IR for these builtins was untested before this patch.

Originally, the code used the outdated method of subtracting floating point values from -0.0 as floating point negation.  This patch remedies that.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D76949

Files:
  clang/lib/CodeGen/CGBuiltin.cpp
  clang/test/CodeGen/builtins-ppc-fma.c


Index: clang/test/CodeGen/builtins-ppc-fma.c
===================================================================
--- clang/test/CodeGen/builtins-ppc-fma.c
+++ clang/test/CodeGen/builtins-ppc-fma.c
@@ -0,0 +1,43 @@
+// RUN: %clang_cc1 -triple powerpc64le-gnu-linux \
+// RUN: -target-feature +altivec -Wall -Wno-unused -Werror -emit-llvm %s -o - | FileCheck      \
+// RUN: %s
+
+typedef __attribute__((vector_size(4 * sizeof(float)))) float vec_float;
+typedef __attribute__((vector_size(2 * sizeof(double)))) double vec_double;
+
+volatile vec_double vd;
+volatile vec_float vf;
+
+void test_fma(void) {
+  vf = __builtin_vsx_xvmaddasp(vf, vf, vf);
+  // CHECK: @llvm.fma.v4f32(<4 x float> %{{.*}}, <4 x float> %{{.*}}, <4 x float> %{{.*}})
+
+  vd = __builtin_vsx_xvmaddadp(vd, vd, vd);
+  // CHECK: @llvm.fma.v2f64(<2 x double> %{{.*}}, <2 x double> %{{.*}}, <2 x double> %{{.*}})
+
+  vf = __builtin_vsx_xvnmaddasp(vf, vf, vf);
+  // CHECK: [[RESULT:%[^ ]+]] = call <4 x float> @llvm.fma.v4f32(<4 x float> %{{.*}}, <4 x float> %{{.*}}, <4 x float> %{{.*}})
+  // CHECK: fneg <4 x float> [[RESULT]]
+
+  vd = __builtin_vsx_xvnmaddadp(vd, vd, vd);
+  // CHECK: [[RESULT:%[^ ]+]] = call <2 x double> @llvm.fma.v2f64(<2 x double> %{{.*}}, <2 x double> %{{.*}}, <2 x double> %{{.*}})
+  // CHECK: fneg <2 x double> [[RESULT]]
+
+  vf = __builtin_vsx_xvmsubasp(vf, vf, vf);
+  // CHECK: [[RESULT:%[^ ]+]] fneg <4 x float> %{{.*}}
+  // CHECK: @llvm.fma.v4f32(<4 x float> %{{.*}}, <4 x float> %{{.*}}, <4 x float> [[RESULT]])
+
+  vd = __builtin_vsx_xvmsubadp(vd, vd, vd);
+  // CHECK: fneg <2 x double> [[RESULT]]
+  // CHECK: [[RESULT:%[^ ]+]] = call <2 x double> @llvm.fma.v2f64(<2 x double> %{{.*}}, <2 x double> %{{.*}}, <2 x double> %{{.*}})
+
+  vf = __builtin_vsx_xvnmsubasp(vf, vf, vf);
+  // CHECK: [[RESULT:%[^ ]+]] = fneg <4 x float> %{{.*}}
+  // CHECK: [[RESULT2:%[^ ]+]] = call <4 x float> @llvm.fma.v2f64(<4 x float> %{{.*}}, <4 x float> %{{.*}}, <4 x float> [[RESULT]])
+  // CHECK: fneg <4 x float> [[RESULT2]]
+
+  vd = __builtin_vsx_xvnmsubadp(vd, vd, vd);
+  // CHECK: [[RESULT:%[^ ]+]] = fneg <2 x double> %{{.*}}
+  // CHECK: [[RESULT2:%[^ ]+]] = call <2 x double> @llvm.fma.v2f64(<2 x double> %{{.*}}, <2 x double> %{{.*}}, <2 x double> [[RESULT]])
+  // CHECK: fneg <2 x double> [[RESULT2]]
+}
Index: clang/lib/CodeGen/CGBuiltin.cpp
===================================================================
--- clang/lib/CodeGen/CGBuiltin.cpp
+++ clang/lib/CodeGen/CGBuiltin.cpp
@@ -13083,25 +13083,24 @@
     Value *X = EmitScalarExpr(E->getArg(0));
     Value *Y = EmitScalarExpr(E->getArg(1));
     Value *Z = EmitScalarExpr(E->getArg(2));
-    Value *Zero = llvm::ConstantFP::getZeroValueForNegation(ResultType);
     llvm::Function *F = CGM.getIntrinsic(Intrinsic::fma, ResultType);
     switch (BuiltinID) {
       case PPC::BI__builtin_vsx_xvmaddadp:
       case PPC::BI__builtin_vsx_xvmaddasp:
         return Builder.CreateCall(F, {X, Y, Z});
+
       case PPC::BI__builtin_vsx_xvnmaddadp:
       case PPC::BI__builtin_vsx_xvnmaddasp:
-        return Builder.CreateFSub(Zero,
-                                  Builder.CreateCall(F, {X, Y, Z}), "sub");
+        return Builder.CreateFNeg(Builder.CreateCall(F, {X, Y, Z}), "neg");
+
       case PPC::BI__builtin_vsx_xvmsubadp:
       case PPC::BI__builtin_vsx_xvmsubasp:
-        return Builder.CreateCall(F,
-                                  {X, Y, Builder.CreateFSub(Zero, Z, "sub")});
+        return Builder.CreateCall(F, {X, Y, Builder.CreateFNeg(Z, "neg")});
+
       case PPC::BI__builtin_vsx_xvnmsubadp:
       case PPC::BI__builtin_vsx_xvnmsubasp:
-        Value *FsubRes =
-          Builder.CreateCall(F, {X, Y, Builder.CreateFSub(Zero, Z, "sub")});
-        return Builder.CreateFSub(Zero, FsubRes, "sub");
+        return Builder.CreateFNeg(
+            Builder.CreateCall(F, {X, Y, Builder.CreateFNeg(Z, "neg")}), "neg");
     }
     llvm_unreachable("Unknown FMA operation");
     return nullptr; // Suppress no-return warning


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