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

[qiucf]

Summary

-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.

[zahiraam]

clang/lib/Driver/ToolChains/Clang.cpp

2844

I would expect the same thing should happen with -ffp-model=strict -ffast-math. This change is not enough to accomplish that.

[zahiraam]

clang/lib/Driver/ToolChains/Clang.cpp

3034

FPExceptionBehavior should be set here and in case options::OPT_ffp_model_EQ:

clang/test/Driver/fp-model.c

69

Add a RUN command for '-ffast-math -ffp-model=strict'. I would expect the same warning.
Currently (without your patch) it is generating this non-sense warning:
https://godbolt.org/z/eW679Y7G3

[qiucf]

Update test case

clang/lib/Driver/ToolChains/Clang.cpp

3034

Here's the case when FPExceptionBehavior was set and -ffp-model=fast or -Ofast or -ffast-math` takes effect. Exception behavior needs to be reset.

OptID was changed so OPT_ffp_model_EQ will not be matched in the switch-case.

[zahiraam]

Looks good to me after the additional RUN line mentioned in my comment for Driver/fp-model.c is added. Thanks.

clang/test/Driver/fp-model.c

77

Please add this:
+ RUN: %clang -### -Ofast -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]

[qiucf]

Thanks!

clang/lib/Driver/ToolChains/Clang.cpp

       }
       break;
 
     case options::OPT_Ofast:
       // If -Ofast is the optimization level, then -ffast-math should be enabled
       if (!OFastEnabled)
         continue;
       [[fallthrough]];
     case options::OPT_ffast_math:
       HonorINFs = false;
       HonorNaNs = false;
       MathErrno = false;
       AssociativeMath = true;
       ReciprocalMath = true;
       ApproxFunc = true;
       SignedZeros = false;
       TrappingMath = false;
       RoundingFPMath = false;
+      FPExceptionBehavior = "";
       // If fast-math is set then set the fp-contract mode to fast.
       FPContract = "fast";
       SeenUnsafeMathModeOption = true;
       break;
     case options::OPT_fno_fast_math:
       HonorINFs = true;
       HonorNaNs = true;
       // Turning on -ffast-math (with either flag) removes the need for

           DenormalFPMath == llvm::DenormalMode::getIEEE() &&
           DenormalFP32Math == llvm::DenormalMode::getIEEE() &&
           FPContract.equals("off"))
         // OK: Current Arg doesn't conflict with -ffp-model=strict
         ;
       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;
       }
     }
 
     // If we handled this option claim it
     A->claim();
   }
 
   if (!HonorINFs)

clang/test/CodeGen/ffp-model.c

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

clang/test/Driver/fp-model.c

 // RUN: %clang -### -ffp-model=strict -Ofast -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=WARNf %s
 // WARNf: warning: overriding '-ffp-model=strict' option with '-Ofast' [-Woverriding-t-option]
 
 // RUN: %clang -### -ffp-model=strict -fdenormal-fp-math=preserve-sign,preserve-sign -c %s 2>&1 \
 // 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 -### -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"
 // CHECK-NOROUND: "-fno-rounding-math"
 
 // RUN: %clang -### -frounding-math -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-ROUND --implicit-check-not ffp-exception-behavior=strict %s
 // CHECK-ROUND: "-cc1"

 // CHECK-FPM-PRECISE: "-fno-rounding-math"
 
 // RUN: %clang -### -nostdinc -ffp-model=strict -c %s 2>&1 \
 // RUN:   | FileCheck --check-prefix=CHECK-FPM-STRICT %s
 // CHECK-FPM-STRICT: "-cc1"
 // 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
 // CHECK-FEB-STRICT: "-cc1"
 // CHECK-FEB-STRICT: "-fno-rounding-math"
 // CHECK-FEB-STRICT: "-ffp-exception-behavior=strict"
 
 // RUN: %clang -### -nostdinc -ffp-exception-behavior=maytrap -c %s 2>&1 \