Don't mark scalar integer multiplication as Expand on x86, since x86

has plain one-result scalar integer multiplication instructions.
This avoids expanding such instructions into MUL_LOHI sequences that
must be special-cased at isel time, and avoids the problem with that
code that provented memory operands from being folded.

This fixes PR1874, addressesing the most common case. The uncommon
cases of optimizing multiply-high operations will require work
in DAGCombiner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@47277 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/X86ISelLowering.cpp b/lib/Target/X86/X86ISelLowering.cpp
index 3e1f9428c912600a3ff493d7e86aeb91014ffd95..544401622095a101374c87c68d1163ed3c0c0dbc 100644 (file)
--- a/lib/Target/X86/X86ISelLowering.cpp
+++ b/lib/Target/X86/X86ISelLowering.cpp
@@ -169,35 +169,31 @@ X86TargetLowering::X86TargetLowering(TargetMachine &TM)
     setOperationAction(ISD::BIT_CONVERT      , MVT::i32  , Expand);
   }
 
-  // Scalar integer multiply, multiply-high, divide, and remainder are
+  // Scalar integer multiply-high, divide, and remainder are
   // lowered to use operations that produce two results, to match the
   // available instructions. This exposes the two-result form to trivial
   // CSE, which is able to combine x/y and x%y into a single instruction,
   // for example. The single-result multiply instructions are introduced
   // in X86ISelDAGToDAG.cpp, after CSE, for uses where the the high part
   // is not needed.
-  setOperationAction(ISD::MUL             , MVT::i8    , Expand);
   setOperationAction(ISD::MULHS           , MVT::i8    , Expand);
   setOperationAction(ISD::MULHU           , MVT::i8    , Expand);
   setOperationAction(ISD::SDIV            , MVT::i8    , Expand);
   setOperationAction(ISD::UDIV            , MVT::i8    , Expand);
   setOperationAction(ISD::SREM            , MVT::i8    , Expand);
   setOperationAction(ISD::UREM            , MVT::i8    , Expand);
-  setOperationAction(ISD::MUL             , MVT::i16   , Expand);
   setOperationAction(ISD::MULHS           , MVT::i16   , Expand);
   setOperationAction(ISD::MULHU           , MVT::i16   , Expand);
   setOperationAction(ISD::SDIV            , MVT::i16   , Expand);
   setOperationAction(ISD::UDIV            , MVT::i16   , Expand);
   setOperationAction(ISD::SREM            , MVT::i16   , Expand);
   setOperationAction(ISD::UREM            , MVT::i16   , Expand);
-  setOperationAction(ISD::MUL             , MVT::i32   , Expand);
   setOperationAction(ISD::MULHS           , MVT::i32   , Expand);
   setOperationAction(ISD::MULHU           , MVT::i32   , Expand);
   setOperationAction(ISD::SDIV            , MVT::i32   , Expand);
   setOperationAction(ISD::UDIV            , MVT::i32   , Expand);
   setOperationAction(ISD::SREM            , MVT::i32   , Expand);
   setOperationAction(ISD::UREM            , MVT::i32   , Expand);
-  setOperationAction(ISD::MUL             , MVT::i64   , Expand);
   setOperationAction(ISD::MULHS           , MVT::i64   , Expand);
   setOperationAction(ISD::MULHU           , MVT::i64   , Expand);
   setOperationAction(ISD::SDIV            , MVT::i64   , Expand);
@@ -205,6 +201,11 @@ X86TargetLowering::X86TargetLowering(TargetMachine &TM)
   setOperationAction(ISD::SREM            , MVT::i64   , Expand);
   setOperationAction(ISD::UREM            , MVT::i64   , Expand);
 
+  // 8, 16, and 32-bit plain multiply are legal. And 64-bit multiply
+  // is also legal on x86-64.
+  if (!Subtarget->is64Bit())
+    setOperationAction(ISD::MUL           , MVT::i64   , Expand);
+
   setOperationAction(ISD::BR_JT            , MVT::Other, Expand);
   setOperationAction(ISD::BRCOND           , MVT::Other, Custom);
   setOperationAction(ISD::BR_CC            , MVT::Other, Expand);

diff --git a/test/CodeGen/X86/mul-remat.ll b/test/CodeGen/X86/mul-remat.ll
new file mode 100644 (file)
index 0000000..ffc8cc0
--- /dev/null
+++ b/test/CodeGen/X86/mul-remat.ll
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | llc -march=x86 | grep mov | count 1
+; PR1874
+       
+define i32 @test(i32 %a, i32 %b) {
+entry:
+       %tmp3 = mul i32 %b, %a
+       ret i32 %tmp3
+}