[PATCH] D129954: [CodeGen][inlineasm] assume the flag output of inline asm is boolean value

[Yuanfang Chen via Phabricator via cfe-commits]

ychen created this revision.
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GCC inline asm document says that
"... the general rule is that the output variable must be a scalar
integer, and the value is boolean."

Commit e5c37958f901cc9bec50624dbee85d40143e4bca lowers flag output of
inline asm on X86 with setcc, hence it is guaranteed that the flag
is of boolean value. Clang does not support ARM inline asm flag output
yet so nothing need to be worried about ARM.

See "Flag Output" section at
https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#OutputOperands

Fixes https://github.com/llvm/llvm-project/issues/56568


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D129954

Files:
  clang/lib/CodeGen/CGStmt.cpp
  clang/test/CodeGen/inline-asm-x86-flag-output.c


Index: clang/test/CodeGen/inline-asm-x86-flag-output.c
===================================================================
--- clang/test/CodeGen/inline-asm-x86-flag-output.c
+++ clang/test/CodeGen/inline-asm-x86-flag-output.c
@@ -374,3 +374,18 @@
       : "cx");
   return b;
 }
+
+int test_assume_boolean_flag(long nr, volatile long *addr) {
+  //CHECK-LABEL: @test_assume_boolean_flag
+  //CHECK: = tail call i32 asm "cmp $2,$1", "={@cca},=*m,r,~{cc},~{dirflag},~{fpsr},~{flags}"(i64* elementtype(i64) %addr, i64 %nr)
+  //CHECK: %1 = icmp ult i32 %0, 2
+  //CHECK: call void @llvm.assume(i1 %1)
+  int x;
+  asm("cmp %2,%1"
+      : "=@cca"(x), "=m"(*(volatile long *)(addr))
+      : "r"(nr)
+      : "cc");
+  if (x)
+    return 0;
+  return 1;
+}
Index: clang/lib/CodeGen/CGStmt.cpp
===================================================================
--- clang/lib/CodeGen/CGStmt.cpp
+++ clang/lib/CodeGen/CGStmt.cpp
@@ -2343,6 +2343,7 @@
   std::vector<llvm::Type *> ArgElemTypes;
   std::vector<llvm::Value*> Args;
   llvm::BitVector ResultTypeRequiresCast;
+  llvm::BitVector ResultRegIsFlagReg;
 
   // Keep track of inout constraints.
   std::string InOutConstraints;
@@ -2400,6 +2401,9 @@
       ResultRegQualTys.push_back(QTy);
       ResultRegDests.push_back(Dest);
 
+      bool IsFlagReg = llvm::StringRef(OutputConstraint).startswith("{@cc");
+      ResultRegIsFlagReg.push_back(IsFlagReg);
+
       llvm::Type *Ty = ConvertTypeForMem(QTy);
       const bool RequiresCast = Info.allowsRegister() &&
           (getTargetHooks().isScalarizableAsmOperand(*this, Ty) ||
@@ -2717,10 +2721,21 @@
   // ResultRegDests can be also populated by addReturnRegisterOutputs() above,
   // in which case its size may grow.
   assert(ResultTypeRequiresCast.size() <= ResultRegDests.size());
+  assert(ResultRegIsFlagReg.size() <= ResultRegDests.size());
   for (unsigned i = 0, e = RegResults.size(); i != e; ++i) {
     llvm::Value *Tmp = RegResults[i];
     llvm::Type *TruncTy = ResultTruncRegTypes[i];
 
+    if ((i < ResultRegIsFlagReg.size()) && ResultRegIsFlagReg[i]) {
+      // Target must guarantee the Value `Tmp` here is lowered to a boolean
+      // value.
+      llvm::Constant *OneVal = llvm::ConstantInt::get(Tmp->getType(), 1);
+      llvm::Value *IsBooleanValue =
+          Builder.CreateCmp(llvm::CmpInst::ICMP_ULE, Tmp, OneVal);
+      llvm::Function *FnAssume = CGM.getIntrinsic(llvm::Intrinsic::assume);
+      Builder.CreateCall(FnAssume, IsBooleanValue);
+    }
+
     // If the result type of the LLVM IR asm doesn't match the result type of
     // the expression, do the conversion.
     if (ResultRegTypes[i] != ResultTruncRegTypes[i]) {


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