[PATCH] Add strchr(p, 0) -> p + strlen(p) to SimplifyLibCalls

[Kai Nacke]

Hi everyone!

This patch adds the transformation strchr(p, 0) -> p + strlen(p) to 
SimplifyLibCalls and removes the ToDo comment.

Please review.

Regards,
Kai
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diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 36d2462..7e1abf1 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -493,8 +493,12 @@ struct StrChrOpt : public LibCallOptimization {
     // Otherwise, the character is a constant, see if the first argument is
     // a string literal.  If so, we can constant fold.
     StringRef Str;
-    if (!getConstantStringInfo(SrcStr, Str))
+    if (!getConstantStringInfo(SrcStr, Str)) {
+      if (TD && CharC->isZero()) { // strchr(p, 0) -> p + strlen(p)
+        return B.CreateGEP(SrcStr, EmitStrLen(SrcStr, B, TD, TLI), "strchr");
+      }
       return 0;
+    }
 
     // Compute the offset, make sure to handle the case when we're searching for
     // zero (a weird way to spell strlen).
@@ -2297,8 +2301,6 @@ void LibCallSimplifier::replaceAllUsesWith(Instruction *I, Value *With) const {
 //   * sqrt(Nroot(x)) -> pow(x,1/(2*N))
 //   * sqrt(pow(x,y)) -> pow(|x|,y*0.5)
 //
-// strchr:
-//   * strchr(p, 0) -> strlen(p)
 // tan, tanf, tanl:
 //   * tan(atan(x)) -> x
 //
diff --git a/test/Transforms/InstCombine/strchr-1.ll b/test/Transforms/InstCombine/strchr-1.ll
index d2c9894..f8860e3 100644
--- a/test/Transforms/InstCombine/strchr-1.ll
+++ b/test/Transforms/InstCombine/strchr-1.ll
@@ -63,3 +63,15 @@ define void @test_simplify5() {
   store i8* %dst, i8** @chp
   ret void
 }
+
+define void @test_simplify6(i8* %str) {
+; CHECK: %strlen = call i32 @strlen(i8* %str)
+; CHECK-NOT: call i8* @strchr
+; CHECK: %strchr = getelementptr i8* %str, i32 %strlen
+; CHECK: store i8* %strchr, i8** @chp, align 4
+; CHECK: ret void
+
+  %dst = call i8* @strchr(i8* %str, i32 0)
+  store i8* %dst, i8** @chp
+  ret void
+}