[llvm] r217859 - Fix BasicTTI::getCmpSelInstrCost to deal with illegal vector types

[Hal Finkel]

Author: hfinkel
Date: Mon Sep 15 23:35:50 2014
New Revision: 217859

URL: http://llvm.org/viewvc/llvm-project?rev=217859&view=rev
Log:
Fix BasicTTI::getCmpSelInstrCost to deal with illegal vector types

The default implementation of getCmpSelInstrCost, which provides the cost of
icmp/fcmp/select instructions, did not deal sensibly with illegal vector types
that were scalarized. We'd ask for the legalization cost of the vector type,
which would return something like (4, f64) given an input of <4 x double>, and
we'd then check the TLI status of the ISD opcode on that scalar type. This would
result in querying (ISD::VSELECT, f64), for example. Amusingly enough,
ISD::VSELECT on scalar types is marked as Legal by default (as with most other
operations), and most backends never change this because VSELECT is never
generated on scalars. However, seeing the resulting operation as Legal, we'd
neglect to add the scalarization cost before returning. The result is that we'd
grossly under-estimate the cost of cmps/selects on illegal vector types.

Now, if type legalization clearly results in scalarization, we skip the early
return and add the scalarization cost.

Added:
    llvm/trunk/test/Analysis/CostModel/PowerPC/cmp-expanded.ll
Modified:
    llvm/trunk/lib/CodeGen/BasicTargetTransformInfo.cpp

Modified: llvm/trunk/lib/CodeGen/BasicTargetTransformInfo.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/BasicTargetTransformInfo.cpp?rev=217859&r1=217858&r2=217859&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/BasicTargetTransformInfo.cpp (original)
+++ llvm/trunk/lib/CodeGen/BasicTargetTransformInfo.cpp Mon Sep 15 23:35:50 2014
@@ -468,7 +468,8 @@ unsigned BasicTTI::getCmpSelInstrCost(un
 
   std::pair<unsigned, MVT> LT = TLI->getTypeLegalizationCost(ValTy);
 
-  if (!TLI->isOperationExpand(ISD, LT.second)) {
+  if (!(ValTy->isVectorTy() && !LT.second.isVector()) &&
+      !TLI->isOperationExpand(ISD, LT.second)) {
     // The operation is legal. Assume it costs 1. Multiply
     // by the type-legalization overhead.
     return LT.first * 1;

Added: llvm/trunk/test/Analysis/CostModel/PowerPC/cmp-expanded.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/CostModel/PowerPC/cmp-expanded.ll?rev=217859&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/CostModel/PowerPC/cmp-expanded.ll (added)
+++ llvm/trunk/test/Analysis/CostModel/PowerPC/cmp-expanded.ll Mon Sep 15 23:35:50 2014
@@ -0,0 +1,14 @@
+; RUN: opt < %s -cost-model -analyze -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 -mattr=-vsx | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define void @exts() {
+
+   ; VSX is disabled, so this cost needs to include scalarization (because
+   ; <4 x double> is legalized to scalars).
+   ; CHECK: cost of 44 {{.*}} fcmp
+   %v1 = fcmp ugt <4 x double> undef, undef
+
+  ret void
+}
+