Support output constraints on "asm goto"
Summary:
Clang's "asm goto" feature didn't initially support outputs constraints. That
was the same behavior as gcc's implementation. The decision by gcc not to
support outputs was based on a restriction in their IR regarding terminators.
LLVM doesn't restrict terminators from returning values (e.g. 'invoke'), so
it made sense to support this feature.
Output values are valid only on the 'fallthrough' path. If an output value's used
on an indirect branch, then it's 'poisoned'.
In theory, outputs *could* be valid on the 'indirect' paths, but it's very
difficult to guarantee that the original semantics would be retained. E.g.
because indirect labels could be used as data, we wouldn't be able to split
critical edges in situations where two 'callbr' instructions have the same
indirect label, because the indirect branch's destination would no longer be
the same.
Reviewers: jyknight, nickdesaulniers, hfinkel
Reviewed By: jyknight, nickdesaulniers
Subscribers: MaskRay, rsmith, hiraditya, llvm-commits, cfe-commits, craig.topper, rnk
Tags: #clang, #llvm
Differential Revision: https://reviews.llvm.org/D69876
diff --git a/clang/lib/CodeGen/CGStmt.cpp b/clang/lib/CodeGen/CGStmt.cpp
index bf63a1f..a49601f 100644
--- a/clang/lib/CodeGen/CGStmt.cpp
+++ b/clang/lib/CodeGen/CGStmt.cpp
@@ -2211,13 +2211,6 @@
Constraints += InputConstraint;
}
- // Append the "input" part of inout constraints last.
- for (unsigned i = 0, e = InOutArgs.size(); i != e; i++) {
- ArgTypes.push_back(InOutArgTypes[i]);
- Args.push_back(InOutArgs[i]);
- }
- Constraints += InOutConstraints;
-
// Labels
SmallVector<llvm::BasicBlock *, 16> Transfer;
llvm::BasicBlock *Fallthrough = nullptr;
@@ -2225,7 +2218,7 @@
if (const auto *GS = dyn_cast<GCCAsmStmt>(&S)) {
IsGCCAsmGoto = GS->isAsmGoto();
if (IsGCCAsmGoto) {
- for (auto *E : GS->labels()) {
+ for (const auto *E : GS->labels()) {
JumpDest Dest = getJumpDestForLabel(E->getLabel());
Transfer.push_back(Dest.getBlock());
llvm::BlockAddress *BA =
@@ -2236,11 +2229,17 @@
Constraints += ',';
Constraints += 'X';
}
- StringRef Name = "asm.fallthrough";
- Fallthrough = createBasicBlock(Name);
+ Fallthrough = createBasicBlock("asm.fallthrough");
}
}
+ // Append the "input" part of inout constraints last.
+ for (unsigned i = 0, e = InOutArgs.size(); i != e; i++) {
+ ArgTypes.push_back(InOutArgTypes[i]);
+ Args.push_back(InOutArgs[i]);
+ }
+ Constraints += InOutConstraints;
+
// Clobbers
for (unsigned i = 0, e = S.getNumClobbers(); i != e; i++) {
StringRef Clobber = S.getClobber(i);
@@ -2293,9 +2292,9 @@
if (IsGCCAsmGoto) {
llvm::CallBrInst *Result =
Builder.CreateCallBr(IA, Fallthrough, Transfer, Args);
+ EmitBlock(Fallthrough);
UpdateAsmCallInst(cast<llvm::CallBase>(*Result), HasSideEffect, ReadOnly,
ReadNone, S, ResultRegTypes, *this, RegResults);
- EmitBlock(Fallthrough);
} else {
llvm::CallInst *Result =
Builder.CreateCall(IA, Args, getBundlesForFunclet(IA));