From 26ad3eb69d21232c204e76728936f5845ed67474 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 2 May 2014 04:11:45 +0000
Subject: [PATCH] Fold strlen(expr ? "str1" : "str2") to x ? len1 : len2. This
 fires about 330 times in a bootstrap of clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207828 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Transforms/Utils/SimplifyLibCalls.cpp | 15 +++++++++++++++
 test/Transforms/InstCombine/strlen-1.ll   | 12 ++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/lib/Transforms/Utils/SimplifyLibCalls.cpp b/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 903fbb58997..0fd185816fd 100644
--- a/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -784,10 +784,25 @@ struct StrLenOpt : public LibCallOptimization {
     if (uint64_t Len = GetStringLength(Src))
       return ConstantInt::get(CI->getType(), Len-1);
 
+    // strlen(x?"foo":"bars") --> x ? 3 : 4
+    if (SelectInst *SI = dyn_cast<SelectInst>(Src)) {
+      uint64_t LenTrue = GetStringLength(SI->getTrueValue());
+      uint64_t LenFalse = GetStringLength(SI->getFalseValue());
+      if (LenTrue && LenFalse) {
+        Context->emitOptimizationRemark(
+            "simplify-libcalls", *Caller, SI->getDebugLoc(),
+            "folded strlen(select) to select of constants");
+        return B.CreateSelect(SI->getCondition(),
+                              ConstantInt::get(CI->getType(), LenTrue-1),
+                              ConstantInt::get(CI->getType(), LenFalse-1));
+      }
+    }
+
     // strlen(x) != 0 --> *x != 0
     // strlen(x) == 0 --> *x == 0
     if (isOnlyUsedInZeroEqualityComparison(CI))
       return B.CreateZExt(B.CreateLoad(Src, "strlenfirst"), CI->getType());
+
     return nullptr;
   }
 };
diff --git a/test/Transforms/InstCombine/strlen-1.ll b/test/Transforms/InstCombine/strlen-1.ll
index 4fa5b4fdb62..4a3caf28a0f 100644
--- a/test/Transforms/InstCombine/strlen-1.ll
+++ b/test/Transforms/InstCombine/strlen-1.ll
@@ -5,6 +5,7 @@
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 
 @hello = constant [6 x i8] c"hello\00"
+@longer = constant [7 x i8] c"longer\00"
 @null = constant [1 x i8] zeroinitializer
 @null_hello = constant [7 x i8] c"\00hello\00"
 @nullstring = constant i8 0
@@ -85,6 +86,17 @@ define i1 @test_simplify8() {
 ; CHECK-NEXT: ret i1 false
 }
 
+define i32 @test_simplify9(i1 %x) {
+; CHECK-LABEL: @test_simplify9
+  %hello = getelementptr [6 x i8]* @hello, i32 0, i32 0
+  %longer = getelementptr [7 x i8]* @longer, i32 0, i32 0
+  %s = select i1 %x, i8* %hello, i8* %longer
+  %l = call i32 @strlen(i8* %s)
+; CHECK-NEXT: select i1 %x, i32 5, i32 6
+  ret i32 %l
+; CHECK-NEXT: ret
+}
+
 ; Check cases that shouldn't be simplified.
 
 define i32 @test_no_simplify1() {
-- 
2.34.1