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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217859 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/BasicTargetTransformInfo.cpp b/lib/CodeGen/BasicTargetTransformInfo.cpp
index 3e0e09e658e0fea0377321c93c2ff2df34057672..e79f458efbf9219c599d5ad350ca56f93a3822df 100644 (file)
--- a/lib/CodeGen/BasicTargetTransformInfo.cpp
+++ b/lib/CodeGen/BasicTargetTransformInfo.cpp
@@ -468,7 +468,8 @@ unsigned BasicTTI::getCmpSelInstrCost(unsigned Opcode, Type *ValTy,
 
   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;

diff --git a/test/Analysis/CostModel/PowerPC/cmp-expanded.ll b/test/Analysis/CostModel/PowerPC/cmp-expanded.ll
new file mode 100644 (file)
index 0000000..38c8439
--- /dev/null
+++ b/test/Analysis/CostModel/PowerPC/cmp-expanded.ll
@@ -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
+}
+