Optimize a printf with a double procent to putchar.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@268922 91177308-0d34-0410-b5e6-96231b3b80d8

Author: jsonn

lib/Transforms/Utils/SimplifyLibCalls.cpp

@@ -1598,8 +1598,8 @@ Value *LibCallSimplifier::optimizePrintFString(CallInst *CI, IRBuilder<> &B) {
   if (!CI->use_empty())
     return nullptr;
 
-  // printf("x") -> putchar('x'), even for '%'.
-  if (FormatStr.size() == 1)
+  // printf("x") -> putchar('x'), even for "%" and "%%".
+  if (FormatStr.size() == 1 || FormatStr == "%%")
     return emitPutChar(B.getInt32(FormatStr[0]), B, TLI);
 
   // printf("%s", "a") --> putchar('a')

test/Transforms/InstCombine/printf-1.ll

@@ -7,6 +7,7 @@ target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f3
 
 @hello_world = constant [13 x i8] c"hello world\0A\00"
 @h = constant [2 x i8] c"h\00"
+@h2 = constant [3 x i8] c"%%\00"
 @percent = constant [2 x i8] c"%\00"
 @percent_c = constant [3 x i8] c"%c\00"
 @percent_d = constant [3 x i8] c"%d\00"
@@ -38,6 +39,17 @@ define void @test_simplify2() {
 ; CHECK-NEXT: ret void
 }
 
+; Special case: printf("%%") -> putchar('%').
+
+define void @test_simplify2b() {
+; CHECK-LABEL: @test_simplify2b(
+  %fmt = getelementptr [3 x i8], [3 x i8]* @h2, i32 0, i32 0
+  call i32 (i8*, ...) @printf(i8* %fmt)
+; CHECK-NEXT: call i32 @putchar(i32 37)
+  ret void
+; CHECK-NEXT: ret void
+}
+
 define void @test_simplify3() {
 ; CHECK-LABEL: @test_simplify3(
   %fmt = getelementptr [2 x i8], [2 x i8]* @percent, i32 0, i32 0