From a0372dec261d137973b29ed14376230c372b4290 Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper@gmail.com>
Date: Wed, 14 Dec 2016 03:17:27 +0000
Subject: [PATCH] [X86][InstCombine] Teach SimplifyDemandedVectorElts to handle
 scalar min/max/cmp intrinsics more correctly.

Now we only pass bit 0 of the DemandedElts to optimize operand 1 as we recurse since the upper bits are unused.

Also calculate UndefElts correctly.

Simplify InstCombineCalls for these instrinics to just call SimplifyDemandedVectorElts for the call instrution to reuse this support.

llvm-svn: 289628
---
 .../Transforms/InstCombine/InstCombineCalls.cpp    | 23 +++++-----------
 .../InstCombine/InstCombineSimplifyDemanded.cpp    | 31 +++++++++++++++++++---
 2 files changed, 34 insertions(+), 20 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 62e2de7..4c41484 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -1760,23 +1760,6 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     break;
   }
 
-  case Intrinsic::x86_sse_min_ss:
-  case Intrinsic::x86_sse_max_ss:
-  case Intrinsic::x86_sse_cmp_ss:
-  case Intrinsic::x86_sse2_min_sd:
-  case Intrinsic::x86_sse2_max_sd:
-  case Intrinsic::x86_sse2_cmp_sd: {
-    // These intrinsics only demand the lowest element of the second input
-    // vector.
-    Value *Arg1 = II->getArgOperand(1);
-    unsigned VWidth = Arg1->getType()->getVectorNumElements();
-    if (Value *V = SimplifyDemandedVectorEltsLow(Arg1, VWidth, 1)) {
-      II->setArgOperand(1, V);
-      return II;
-    }
-    break;
-  }
-
   case Intrinsic::x86_fma_vfmadd_ss:
   case Intrinsic::x86_fma_vfmsub_ss:
   case Intrinsic::x86_fma_vfnmadd_ss:
@@ -1837,6 +1820,12 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
     break;
   }
 
+  case Intrinsic::x86_sse_cmp_ss:
+  case Intrinsic::x86_sse_min_ss:
+  case Intrinsic::x86_sse_max_ss:
+  case Intrinsic::x86_sse2_cmp_sd:
+  case Intrinsic::x86_sse2_min_sd:
+  case Intrinsic::x86_sse2_max_sd:
   case Intrinsic::x86_xop_vfrcz_ss:
   case Intrinsic::x86_xop_vfrcz_sd: {
    unsigned VWidth = II->getType()->getVectorNumElements();
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 979163c..3038fd5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -1290,14 +1290,39 @@ Value *InstCombiner::SimplifyDemandedVectorElts(Value *V, APInt DemandedElts,
       // checks).
       break;
 
-    // Binary scalar-as-vector operations that work column-wise.  A dest element
-    // is a function of the corresponding input elements from the two inputs.
+    // Binary scalar-as-vector operations that work column-wise. The high
+    // elements come from operand 0. The low element is a function of both
+    // operands.
     case Intrinsic::x86_sse_min_ss:
     case Intrinsic::x86_sse_max_ss:
     case Intrinsic::x86_sse_cmp_ss:
     case Intrinsic::x86_sse2_min_sd:
     case Intrinsic::x86_sse2_max_sd:
-    case Intrinsic::x86_sse2_cmp_sd:
+    case Intrinsic::x86_sse2_cmp_sd: {
+      TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
+                                        UndefElts, Depth + 1);
+      if (TmpV) { II->setArgOperand(0, TmpV); MadeChange = true; }
+
+      // If lowest element of a scalar op isn't used then use Arg0.
+      if (!DemandedElts[0])
+        return II->getArgOperand(0);
+
+      // Only lower element is used for operand 1.
+      DemandedElts = 1;
+      TmpV = SimplifyDemandedVectorElts(II->getArgOperand(1), DemandedElts,
+                                        UndefElts2, Depth + 1);
+      if (TmpV) { II->setArgOperand(1, TmpV); MadeChange = true; }
+
+      // Lower element is undefined if both lower elements are undefined.
+      // Consider things like undef&0.  The result is known zero, not undef.
+      if (!UndefElts2[0])
+        UndefElts.clearBit(0);
+
+      break;
+    }
+
+    // Binary scalar-as-vector operations that work column-wise.  A dest element
+    // is a function of the corresponding input elements from the two inputs.
     case Intrinsic::x86_sse41_round_ss:
     case Intrinsic::x86_sse41_round_sd:
       TmpV = SimplifyDemandedVectorElts(II->getArgOperand(0), DemandedElts,
-- 
2.7.4