Add comments and test case for [X86TTI] Make constant base pointers for GetElementPtr...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205468 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86TargetTransformInfo.cpp b/lib/Target/X86/X86TargetTransformInfo.cpp
index 437f63d3280bd6ac423fd31562976b54727cc8d9..c04964d60bfcb88eaaecb1a2cd08623b4ce1be81 100644 (file)
--- a/lib/Target/X86/X86TargetTransformInfo.cpp
+++ b/lib/Target/X86/X86TargetTransformInfo.cpp
@@ -915,6 +915,9 @@ unsigned X86TTI::getIntImmCost(unsigned Opcode, unsigned Idx, const APInt &Imm,
   switch (Opcode) {
   default: return TCC_Free;
   case Instruction::GetElementPtr:
+    // Always hoist the base address of a GetElementPtr. This prevents the
+    // creation of new constants for every base constant that gets constant
+    // folded with the offset.
     if (Idx == 0)
       return 2 * TCC_Basic;
     return TCC_Free;

diff --git a/test/Transforms/ConstantHoisting/X86/const-base-addr.ll b/test/Transforms/ConstantHoisting/X86/const-base-addr.ll
new file mode 100644 (file)
index 0000000..ffd51b5
--- /dev/null
+++ b/test/Transforms/ConstantHoisting/X86/const-base-addr.ll
@@ -0,0 +1,24 @@
+; RUN: opt -S -consthoist < %s | FileCheck %s
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-macosx10.9.0"
+
+%T = type { i32, i32, i32, i32 }
+
+; Test if even cheap base addreses are hoisted.
+define i32 @test1() nounwind {
+; CHECK-LABEL:  @test1
+; CHECK:        %const = bitcast i32 12345678 to i32
+; CHECK:        %1 = inttoptr i32 %const to %T*
+; CHECK:        %addr1 = getelementptr %T* %1, i32 0, i32 1
+  %addr1 = getelementptr %T* inttoptr (i32 12345678 to %T*), i32 0, i32 1
+  %tmp1 = load i32* %addr1
+  %addr2 = getelementptr %T* inttoptr (i32 12345678 to %T*), i32 0, i32 2
+  %tmp2 = load i32* %addr2
+  %addr3 = getelementptr %T* inttoptr (i32 12345678 to %T*), i32 0, i32 3
+  %tmp3 = load i32* %addr3
+  %tmp4 = add i32 %tmp1, %tmp2
+  %tmp5 = add i32 %tmp3, %tmp4
+  ret i32 %tmp5
+}
+