[PATCH] Do not optimise fprintf() calls if its return value is used.

[Peter Collingbourne]

http://llvm-reviews.chandlerc.com/D620

Files:
  lib/Transforms/Utils/SimplifyLibCalls.cpp
  test/Transforms/InstCombine/fprintf-1.ll

Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1518,6 +1518,12 @@
     if (!getConstantStringInfo(CI->getArgOperand(1), FormatStr))
       return 0;
 
+    // Do not do any of the following transformations if the fprintf return
+    // value is used, in general the fprintf return value is not compatible
+    // with fwrite(), fputc() or fputs().
+    if (!CI->use_empty())
+      return 0;
+
     // fprintf(F, "foo") --> fwrite("foo", 3, 1, F)
     if (CI->getNumArgOperands() == 2) {
       for (unsigned i = 0, e = FormatStr.size(); i != e; ++i)
@@ -1527,11 +1533,10 @@
       // These optimizations require DataLayout.
       if (!TD) return 0;
 
-      Value *NewCI = EmitFWrite(CI->getArgOperand(1),
-                                ConstantInt::get(TD->getIntPtrType(*Context),
-                                                 FormatStr.size()),
-                                CI->getArgOperand(0), B, TD, TLI);
-      return NewCI ? ConstantInt::get(CI->getType(), FormatStr.size()) : 0;
+      return EmitFWrite(CI->getArgOperand(1),
+                        ConstantInt::get(TD->getIntPtrType(*Context),
+                                         FormatStr.size()),
+                        CI->getArgOperand(0), B, TD, TLI);
     }
 
     // The remaining optimizations require the format string to be "%s" or "%c"
@@ -1544,14 +1549,12 @@
     if (FormatStr[1] == 'c') {
       // fprintf(F, "%c", chr) --> fputc(chr, F)
       if (!CI->getArgOperand(2)->getType()->isIntegerTy()) return 0;
-      Value *NewCI = EmitFPutC(CI->getArgOperand(2), CI->getArgOperand(0), B,
-                               TD, TLI);
-      return NewCI ? ConstantInt::get(CI->getType(), 1) : 0;
+      return EmitFPutC(CI->getArgOperand(2), CI->getArgOperand(0), B, TD, TLI);
     }
 
     if (FormatStr[1] == 's') {
       // fprintf(F, "%s", str) --> fputs(str, F)
-      if (!CI->getArgOperand(2)->getType()->isPointerTy() || !CI->use_empty())
+      if (!CI->getArgOperand(2)->getType()->isPointerTy())
         return 0;
       return EmitFPutS(CI->getArgOperand(2), CI->getArgOperand(0), B, TD, TLI);
     }
Index: test/Transforms/InstCombine/fprintf-1.ll
===================================================================
--- test/Transforms/InstCombine/fprintf-1.ll
+++ test/Transforms/InstCombine/fprintf-1.ll
@@ -78,3 +78,12 @@
   ret void
 ; CHECK-NEXT: ret void
 }
+
+define i32 @test_no_simplify3(%FILE* %fp) {
+; CHECK: @test_no_simplify3
+  %fmt = getelementptr [13 x i8]* @hello_world, i32 0, i32 0
+  %1 = call i32 (%FILE*, i8*, ...)* @fprintf(%FILE* %fp, i8* %fmt)
+; CHECK-NEXT: call i32 (%FILE*, i8*, ...)* @fprintf(%FILE* %fp, i8* getelementptr inbounds ([13 x i8]* @hello_world, i32 0, i32 0))
+  ret i32 %1
+; CHECK-NEXT: ret i32 %1
+}
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