[PATCH] D17490: [InstCombine][SSE] Demanded vector elements for scalar intrinsics

[Simon Pilgrim via llvm-commits]

RKSimon added inline comments.

================
Comment at: lib/Transforms/InstCombine/InstCombineCalls.cpp:1374-1389
@@ -1339,1 +1373,18 @@
 
+  case Intrinsic::x86_sse41_round_ss:
+  case Intrinsic::x86_sse41_round_sd: {
+    // These intrinsics demand the upper elements of the first input vector and
+    // the lowest element of the second input vector.
+    bool MadeChange = false;
+    Value *Arg0 = II->getArgOperand(0);
+    Value *Arg1 = II->getArgOperand(1);
+    unsigned VWidth = Arg0->getType()->getVectorNumElements();
+    if (Value *V = SimplifyDemandedVectorEltsHigh(Arg0, VWidth, VWidth - 1)) {
+      II->setArgOperand(0, V);
+      MadeChange = true;
+    }
+    if (Value *V = SimplifyDemandedVectorEltsLow(Arg1, VWidth, 1)) {
+      II->setArgOperand(1, V);
+      MadeChange = true;
+    }
+    if (MadeChange)
----------------
For the binary scalar intrinsics we need all the elements of the first input: the lowest is used in the operation and the remaining are all 'passed through' to the result.

================
Comment at: lib/Transforms/InstCombine/InstCombineCalls.cpp:1406-1409
@@ -1350,6 +1405,6 @@
   case Intrinsic::x86_avx2_psrli_d:
   case Intrinsic::x86_avx2_psrli_q:
   case Intrinsic::x86_avx2_psrli_w:
   case Intrinsic::x86_sse2_pslli_d:
   case Intrinsic::x86_sse2_pslli_q:
   case Intrinsic::x86_sse2_pslli_w:
----------------
I've included the 'MadeChange' bool so we can combine both in one pass. I've also done this in the existing similar COMI/UCOMI combine above.


Repository:
  rL LLVM

http://reviews.llvm.org/D17490