zahiraam created this revision.
zahiraam added reviewers: andrew.w.kaylor, aaron.ballman, thakis, rjmccall,
fhahn.
Herald added a project: All.
zahiraam requested review of this revision.
Herald added a project: clang.
Currently the control of the eval-method is mixed with fast-math.
FLT_EVAL_METHOD tells the user the precision at which, temporary results
are evaluated but when fast-math is enabled, the numeric values are not
guaranteed to match the source semantics, so the eval-method is
meaningless.
For example, the expression `x + y + z` has as source semantics `(x + y) + z`.
FLT_EVAL_METHOD is telling the user at which precision `(x + y)`
is evaluated. With fast-math enable the compiler may choose to evaluate the
expression as `(y + z) + x`.
The correct behavior is to set the FLT_EVAL_METHOD to `-1`, to tell the user
that the precision of the intermediate values is unknow.
This patch is doing that.
This patch is also fixing a crash when the `pragma clang fp eval-method` is
given the wrong value (should be source, double, extended).
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D121122
Files:
clang/include/clang/Basic/DiagnosticParseKinds.td
clang/lib/Lex/PPMacroExpansion.cpp
clang/lib/Sema/Sema.cpp
clang/lib/Sema/SemaAttr.cpp
clang/test/CodeGen/eval-method-fast-math.c
clang/test/Sema/fp-eval-pragma.cpp
Index: clang/test/Sema/fp-eval-pragma.cpp
===================================================================
--- clang/test/Sema/fp-eval-pragma.cpp
+++ clang/test/Sema/fp-eval-pragma.cpp
@@ -27,6 +27,16 @@
return 0;
}
+void apply_pragma_with_wrong_value() {
+ // expected-error@+1{{unexpected argument 'value' to '#pragma clang fp eval_method'; expected 'source' or 'double' or 'extended'}}
+#pragma clang fp eval_method(value)
+}
+
+int foo3() {
+ apply_pragma_with_wrong_value();
+ return 0;
+}
+
void foo() {
auto a = __FLT_EVAL_METHOD__;
{
Index: clang/test/CodeGen/eval-method-fast-math.c
===================================================================
--- /dev/null
+++ clang/test/CodeGen/eval-method-fast-math.c
@@ -0,0 +1,55 @@
+// RUN: %clang_cc1 -fexperimental-strict-floating-point \
+// RUN: -triple x86_64-linux-gnu -emit-llvm -o - %s \
+// RUN: | FileCheck %s -check-prefixes=CHECK
+
+// RUN: %clang_cc1 -triple i386--linux -emit-llvm -o - %s \
+// RUN: | FileCheck %s -check-prefixes=CHECK-EXT
+
+// RUN: %clang_cc1 -fexperimental-strict-floating-point \
+// RUN: -mreassociate -freciprocal-math -ffp-contract=fast \
+// RUN: -ffast-math -triple x86_64-linux-gnu \
+// RUN: -emit-llvm -o - %s \
+// RUN: | FileCheck %s -check-prefixes=CHECK-FAST
+
+// RUN: %clang_cc1 -triple i386--linux -mreassociate -freciprocal-math \
+// RUN: -ffp-contract=fast -ffast-math -emit-llvm -o - %s \
+// RUN: | FileCheck %s -check-prefixes=CHECK-FAST
+
+float res;
+int add(float a, float b, float c) {
+ // CHECK: fadd float
+ // CHECK: load float, float*
+ // CHECK: fadd float
+ // CHECK: store float
+ // CHECK-FAST: fadd fast float
+ // CHECK-FAST: load float, float*
+ // CHECK-FAST: fadd fast float
+ // CHECK: ret i32 0
+ // CHECK-EXT: ret i32 2
+ // CHECK-FAST: ret i32 -1
+ res = a + b + c;
+ return __FLT_EVAL_METHOD__;
+}
+
+int add_precise(float a, float b, float c) {
+#pragma float_control(precise, on)
+ // CHECK: fadd float
+ // CHECK: load float, float*
+ // CHECK: fadd float
+ // CHECK: store float
+ // CHECK: ret i32 0
+ // CHECK-FAST: ret i32 -1
+ res = a + b + c;
+ return __FLT_EVAL_METHOD__;
+}
+
+int add_not_precise(float a, float b, float c) {
+ // Fast-math is enabled with this pragma.
+#pragma float_control(precise, off)
+ // CHECK-FAST: fadd fast float
+ // CHECK-FAST: load float, float*
+ // CHECK-FAST: fadd fast float
+ // CHECK-FAST: ret i32 -1
+ res = a + b + c;
+ return __FLT_EVAL_METHOD__;
+}
Index: clang/lib/Sema/SemaAttr.cpp
===================================================================
--- clang/lib/Sema/SemaAttr.cpp
+++ clang/lib/Sema/SemaAttr.cpp
@@ -517,6 +517,10 @@
else
NewFPFeatures.setFPPreciseEnabled(false);
FpPragmaStack.Act(Loc, Action, StringRef(), NewFPFeatures);
+ // Fast-math is enabled.
+ PP.setCurrentFPEvalMethod(
+ Loc, LangOptions::FPEvalMethodKind::FEM_Indeterminable);
+ PP.getCurrentFPEvalMethod();
break;
case PFC_Except:
if (!isPreciseFPEnabled())
Index: clang/lib/Sema/Sema.cpp
===================================================================
--- clang/lib/Sema/Sema.cpp
+++ clang/lib/Sema/Sema.cpp
@@ -254,6 +254,9 @@
PP.setCurrentFPEvalMethod(SourceLocation(),
getLangOpts().getFPEvalMethod());
CurFPFeatures.setFPEvalMethod(PP.getCurrentFPEvalMethod());
+ // Fast-math is enabled.
+ if (getLangOpts().AllowFPReassoc || getLangOpts().AllowRecip)
+ PP.setCurrentFPEvalMethod(SourceLocation(), LangOptions::FEM_Indeterminable);
}
// Anchor Sema's type info to this TU.
Index: clang/lib/Lex/PPMacroExpansion.cpp
===================================================================
--- clang/lib/Lex/PPMacroExpansion.cpp
+++ clang/lib/Lex/PPMacroExpansion.cpp
@@ -1577,14 +1577,35 @@
Tok.setKind(tok::string_literal);
} else if (II == Ident__FLT_EVAL_METHOD__) {
// __FLT_EVAL_METHOD__ is set to the default value.
- OS << getTUFPEvalMethod();
- // __FLT_EVAL_METHOD__ expands to a simple numeric value.
- Tok.setKind(tok::numeric_constant);
- if (getLastFPEvalPragmaLocation().isValid()) {
- // The program is ill-formed. The value of __FLT_EVAL_METHOD__ is altered
- // by the pragma.
- Diag(Tok, diag::err_illegal_use_of_flt_eval_macro);
- Diag(getLastFPEvalPragmaLocation(), diag::note_pragma_entered_here);
+ if (getTUFPEvalMethod() ==
+ LangOptions::FPEvalMethodKind::FEM_Indeterminable) {
+ // This is possible if we are in a `fast-math` mode (set either
+ // via a command line option or via a `pragam float_conntrol` or a
+ // `pragma clang fp eval-method`.
+ // __FLT_EVAL_METHOD__ expands to -1.
+ // The `minus` operator is the next token we read from the stream.
+ auto Toks = std::make_unique<Token[]>(2);
+ OS << "-";
+ Tok.setKind(tok::minus);
+ // Push the token `1` to the stream.
+ Token NumberToken;
+ NumberToken.startToken();
+ NumberToken.setKind(tok::numeric_constant);
+ NumberToken.setLiteralData("1");
+ NumberToken.setLength(1);
+ Toks[0] = NumberToken;
+ EnterTokenStream(std::move(Toks), 1, /*DisableMacroExpansion*/ false,
+ /*IsReinject*/ false);
+ } else {
+ OS << getTUFPEvalMethod();
+ // __FLT_EVAL_METHOD__ expands to a simple numeric value.
+ Tok.setKind(tok::numeric_constant);
+ if (getLastFPEvalPragmaLocation().isValid()) {
+ // The program is ill-formed. The value of __FLT_EVAL_METHOD__ is
+ // altered by the pragma.
+ Diag(Tok, diag::err_illegal_use_of_flt_eval_macro);
+ Diag(getLastFPEvalPragmaLocation(), diag::note_pragma_entered_here);
+ }
}
} else if (II == Ident__COUNTER__) {
// __COUNTER__ expands to a simple numeric value.
Index: clang/include/clang/Basic/DiagnosticParseKinds.td
===================================================================
--- clang/include/clang/Basic/DiagnosticParseKinds.td
+++ clang/include/clang/Basic/DiagnosticParseKinds.td
@@ -1489,7 +1489,8 @@
"%select{"
"'fast' or 'on' or 'off'|"
"'on' or 'off'|"
- "'ignore', 'maytrap' or 'strict'}2">;
+ "'ignore', 'maytrap' or 'strict'|"
+ "'source' or 'double' or 'extended'}2">;
def err_pragma_invalid_keyword : Error<
"invalid argument; expected 'enable'%select{|, 'full'}0%select{|, 'assume_safety'}1 or 'disable'">;
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