From 718ada97bcd0007dcb9c6a0ea86e4be88c9d4b6b Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 2 May 2014 04:11:45 +0000
Subject: Fold strlen(expr ? "str1" : "str2") to x ? len1 : len2. This fires
 about 330 times in a bootstrap of clang.

llvm-svn: 207828
---
 llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

(limited to 'llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp')

diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 903fbb58997..0fd185816fd 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/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;
   }
 };
-- 
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