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[clang] Set FPOptions at the beginning of CompoundStmt #111654

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[clang] Set FPOptions at the beginning of CompoundStmt #111654

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a472163
[clang] Set FPOptions at the beginning of CompoundStmt
spavloff Oct 9, 2024
63ccc17
Rename getInsideFPOptions to getActiveFPOptions
spavloff Nov 11, 2024
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9 changes: 9 additions & 0 deletions clang/include/clang/AST/Stmt.h
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Original file line number Diff line number Diff line change
Expand Up @@ -1684,6 +1684,15 @@ class CompoundStmt final
return hasStoredFPFeatures() ? getStoredFPFeatures() : FPOptionsOverride();
}

/// Get FPOptions active inside this statement. They may differ from the outer
/// options due to pragmas.
/// \param CurFPOptions FPOptions outside this statement.
FPOptions getActiveFPOptions(FPOptions CurFPOptions) const {
return hasStoredFPFeatures()
? getStoredFPFeatures().applyOverrides(CurFPOptions)
: CurFPOptions;
}

using body_iterator = Stmt **;
using body_range = llvm::iterator_range<body_iterator>;

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5 changes: 5 additions & 0 deletions clang/lib/CodeGen/CGStmt.cpp
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Expand Up @@ -522,6 +522,11 @@ CodeGenFunction::EmitCompoundStmtWithoutScope(const CompoundStmt &S,
assert((!GetLast || (GetLast && ExprResult)) &&
"If GetLast is true then the CompoundStmt must have a StmtExprResult");

// Optionally set up the new FP environment, if the compound statement
// contains a pragma that modifies it.
FPOptions NewFP = S.getActiveFPOptions(CurFPFeatures);
CGFPOptionsRAII SavedFPFeatues(*this, NewFP);

Address RetAlloca = Address::invalid();

for (auto *CurStmt : S.body()) {
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18 changes: 17 additions & 1 deletion clang/test/CodeGen/fast-math.c
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@@ -1,4 +1,4 @@
// RUN: %clang_cc1 -ffast-math -ffp-contract=fast -emit-llvm -o - %s | FileCheck %s
// RUN: %clang_cc1 -ffast-math -ffp-contract=fast -emit-llvm -O2 -o - %s | FileCheck %s
float f0, f1, f2;
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It seems to me that this issue exists only at O2, right? https://godbolt.org/z/xGcWG1aM6
Shouldn't that be reflected in the code somewhere?

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Yes, this fact is reflected in #84648. Actually the problem is incorrect optimization caused by wrong fast-math flags.

Also your example cannot demonstrate the issue because it is C++ code. In C++ mode instructions like SelectInst or PHINode do not get fast-math flags.


void foo(void) {
Expand All @@ -9,3 +9,19 @@ void foo(void) {

// CHECK: ret
}

float issue_84648a(float *x) {
return x[0] == x[1] ? x[1] : x[0];
}

// CHECK-LABEL: define{{.*}} float @issue_84648a(ptr {{.*}})
// CHECK: [[VAL:%.+]] = load float, ptr
// CHECK: ret float [[VAL]]

float issue_84648b(float *x) {
#pragma float_control(precise, on)
return x[0] == x[1] ? x[1] : x[0];
}

// CHECK-LABEL: define{{.*}} float @issue_84648b(ptr{{.*}} %x)
// CHECK: fcmp oeq
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