[llvm] r280928 - [Thumb1] Fix cost calculation for complemented immediates

[James Molloy via llvm-commits]

Author: jamesm
Date: Thu Sep  8 07:58:04 2016
New Revision: 280928

URL: http://llvm.org/viewvc/llvm-project?rev=280928&view=rev
Log:
[Thumb1] Fix cost calculation for complemented immediates

Materializing something like "-3" can be done as 2 instructions:
  MOV r0, #3
  MVN r0, r0

This has a cost of 2, not 3. It looks like we were already trying to detect this pattern in TII::getIntImmCost(), but were taking the complement of the zero-extended value instead of the sign-extended value which is unlikely to ever produce a number < 256.

There were no tests failing after changing this... :/

Added:
    llvm/trunk/test/CodeGen/ARM/immcost.ll
Modified:
    llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp?rev=280928&r1=280927&r2=280928&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMTargetTransformInfo.cpp Thu Sep  8 07:58:04 2016
@@ -41,7 +41,7 @@ int ARMTTIImpl::getIntImmCost(const APIn
   // Thumb1.
   if (SImmVal >= 0 && SImmVal < 256)
     return 1;
-  if ((~ZImmVal < 256) || ARM_AM::isThumbImmShiftedVal(ZImmVal))
+  if ((~SImmVal < 256) || ARM_AM::isThumbImmShiftedVal(ZImmVal))
     return 2;
   // Load from constantpool.
   return 3;

Added: llvm/trunk/test/CodeGen/ARM/immcost.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/immcost.ll?rev=280928&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/immcost.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/immcost.ll Thu Sep  8 07:58:04 2016
@@ -0,0 +1,21 @@
+; RUN: llc %s -o - -O1 -debug-only=consthoist 2>&1 | FileCheck %s
+; REQUIRES: asserts
+
+target datalayout = "e-m:o-p:32:32-f64:32:64-v64:32:64-v128:32:128-a:0:32-n32-S32"
+target triple = "thumbv6m-apple-ios8.0.0"
+
+declare void @g(i32)
+
+; CHECK: Collect constant i32 -3 from   call void @g(i32 -3) with cost 2
+define void @f(i1 %cond) {
+entry:
+  call void @g(i32 -3)
+  br i1 %cond, label %true, label %ret
+
+true:
+  call void @g(i32 -3)
+  br label %ret
+
+ret:
+  ret void
+}