[Clang] Fix behavior of -ffp-model option when overriden

-ffp-model=strict -ffp-model=fast will still enable strict exception
handling behavior, therefore clang still emits constrained FP operations
in IR.

-ffp-model=fast -ffp-model=strict emits two warnings: one for strict
overriding fast, the other for strict overriding strict, which is
confusing.

Reviewed By: zahiraam

Differential Revision: https://reviews.llvm.org/D137618

Author: ecnelises

clang/lib/Driver/ToolChains/Clang.cpp

@@ -3041,6 +3041,7 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       SignedZeros = false;
       TrappingMath = false;
       RoundingFPMath = false;
+      FPExceptionBehavior = "";
       // If fast-math is set then set the fp-contract mode to fast.
       FPContract = "fast";
       SeenUnsafeMathModeOption = true;
@@ -3081,10 +3082,12 @@ static void RenderFloatingPointOptions(const ToolChain &TC, const Driver &D,
       else {
         StrictFPModel = false;
         FPModel = "";
-        D.Diag(clang::diag::warn_drv_overriding_flag_option)
-            << "-ffp-model=strict" <<
-            ((A->getNumValues() == 0) ?  A->getSpelling()
-            : Args.MakeArgString(A->getSpelling() + A->getValue()));
+        auto RHS = (A->getNumValues() == 0)
+                       ? A->getSpelling()
+                       : Args.MakeArgString(A->getSpelling() + A->getValue());
+        if (RHS != "-ffp-model=strict")
+          D.Diag(clang::diag::warn_drv_overriding_flag_option)
+              << "-ffp-model=strict" << RHS;
       }
     }
 

clang/test/CodeGen/ffp-model.c

@@ -36,9 +36,9 @@ float mymuladd(float x, float y, float z) {
 
   // CHECK-STRICT-FAST: load float, ptr
   // CHECK-STRICT-FAST: load float, ptr
-  // CHECK-STRICT-FAST: call fast float @llvm.experimental.constrained.fmul.f32(float {{.*}}, float {{.*}}, {{.*}})
+  // CHECK-STRICT-FAST: fmul fast float {{.*}}, {{.*}}
   // CHECK-STRICT-FAST: load float, ptr
-  // CHECK-STRICT-FAST: call fast float @llvm.experimental.constrained.fadd.f32(float {{.*}}, float {{.*}}, {{.*}}
+  // CHECK-STRICT-FAST: fadd fast float {{.*}}, {{.*}}
 
   // CHECK-FAST1: load float, ptr
   // CHECK-FAST1: load float, ptr

clang/test/Driver/fp-model.c

@@ -66,6 +66,17 @@
 // RUN:   | FileCheck --check-prefix=WARN10 %s
 // WARN10: warning: overriding '-ffp-model=strict' option with '-fdenormal-fp-math=preserve-sign,preserve-sign' [-Woverriding-t-option]
 
+// RUN: %clang -### -ffp-model=fast -ffp-model=strict -c %s 2>&1 | FileCheck \
+// RUN:   --check-prefix=WARN11 %s
+// WARN11: warning: overriding '-ffp-model=fast' option with '-ffp-model=strict' [-Woverriding-t-option]
+// WARN11-NOT: warning: overriding '-ffp-model=strict' option with '-ffp-model=strict' [-Woverriding-t-option]
+
+// RUN: %clang -### -Ofast -ffp-model=strict -c %s 2>&1 | FileCheck \
+// RUN:   --check-prefix=WARN12 %s
+// RUN: %clang -### -ffast-math -ffp-model=strict -c %s 2>&1 | FileCheck \
+// RUN:   --check-prefix=WARN12 %s
+// WARN12-NOT: warning: overriding '-ffp-model=strict' option with '-ffp-model=strict' [-Woverriding-t-option]
+
 // RUN: %clang -### -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-NOROUND %s
 // CHECK-NOROUND: "-cc1"
@@ -107,6 +118,13 @@
 // CHECK-FPM-STRICT: "-frounding-math"
 // CHECK-FPM-STRICT: "-ffp-exception-behavior=strict"
 
+// RUN: %clang -### -nostdinc -ffp-model=strict -ffp-model=fast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-EXCEPT %s
+// RUN: %clang -### -nostdinc -ffp-model=strict -ffast-math -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-EXCEPT %s
+// RUN: %clang -### -nostdinc -ffp-model=strict -Ofast -c %s 2>&1 \
+// RUN:   | FileCheck --check-prefix=CHECK-NO-EXCEPT %s
+// CHECK-NO-EXCEPT-NOT: "-ffp-exception-behavior=strict"
 
 // RUN: %clang -### -nostdinc -ffp-exception-behavior=strict -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FEB-STRICT %s