[llvm] r207828 - Fold strlen(expr ? "str1" : "str2") to x ? len1 : len2. This fires about 330 times in a bootstrap of clang.

[Nick Lewycky]

Author: nicholas
Date: Thu May  1 23:11:45 2014
New Revision: 207828

URL: http://llvm.org/viewvc/llvm-project?rev=207828&view=rev
Log:
Fold strlen(expr ? "str1" : "str2") to x ? len1 : len2. This fires about 330 times in a bootstrap of clang.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
    llvm/trunk/test/Transforms/InstCombine/strlen-1.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp?rev=207828&r1=207827&r2=207828&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp Thu May  1 23:11:45 2014
@@ -784,10 +784,25 @@ struct StrLenOpt : public LibCallOptimiz
     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;
   }
 };

Modified: llvm/trunk/test/Transforms/InstCombine/strlen-1.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/strlen-1.ll?rev=207828&r1=207827&r2=207828&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/strlen-1.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/strlen-1.ll Thu May  1 23:11:45 2014
@@ -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"
+ at 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() {