[llvm-commits] [llvm-gcc] llvm-gcc patch for PR1582 (review only)

[Zhou Sheng]

Hi All,

This patch is for PR1582. As recent discuss on that pr, the C++ FE doesn't
track the restrict qualifier in the function declaration at all. When
llvm-gcc handling CALL_EXPR and emiting callInst instruction, it can't get
the "NoAlias" attribute, and hence insert a BitCast in CallInst. This patch
is to eliminate this bitcast.

Testcase attached here also.

Index: llvm-convert.cpp
===================================================================
--- llvm-convert.cpp	(revision 43895)
+++ llvm-convert.cpp	(working copy)
@@ -2846,8 +2846,16 @@
   // to:
   //   %tmp = call float @foo( )
   // This commonly occurs due to C "implicit ..." semantics.
+  //
+  // Or
+  //
+  //   call void bitcast (void (i32* noalias)* @foo to void (i32*)*)(i32* %x)
+  // to:
+  //   call void @foo(i32* %x noalias)
+  // This occurs due to C++ FE doesn't track the restrict qualifier 
+  // in the function declaration at all.
   if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Callee)) {
-    if (CallOperands.empty() && CE->getOpcode() == Instruction::BitCast) {
+    if (CE->getOpcode() == Instruction::BitCast) {
       Constant *RealCallee = CE->getOperand(0);
       assert(isa<PointerType>(RealCallee->getType()) &&
              "Bitcast to ptr not from ptr?");
@@ -2858,8 +2866,20 @@
         const FunctionType *ActualFT =
           cast<FunctionType>(ActualPT->getElementType());
         if (RealFT->getReturnType() == ActualFT->getReturnType() &&
-            ActualFT->getNumParams() == 0)
+            ActualFT->getNumParams() == 0 && CallOperands.empty())
           Callee = RealCallee;
+        else if (RealFT->getReturnType() == ActualFT->getReturnType() &&
+                 RealFT->getNumParams() == ActualFT->getNumParams() &&
+                 RealFT->getNumParams() == CallOperands.size()) {
+          bool isSame = true;
+          for (unsigned i = 0; i < RealFT->getNumParams(); ++i)
+            if (RealFT->getParamType(i) != ActualFT->getParamType(i)) {
+              isSame = false;
+              break;
+            }
+          if (isSame)
+            Callee = RealCallee;
+        }
       }
     }
   }

// RUN: %llvmgxx -c -emit-llvm %s -o - | llvm-dis | grep call | not grep bitcast

void foo(int * __restrict myptr1, int * myptr2) {
  myptr1[0] = 0;
  myptr2[0] = 0;
}

int main() {
  int x, y;
  foo(&x, &y);
  return 0;
}

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