From: Simon Pilgrim <llvm-dev@redking.me.uk>
Date: Wed, 15 Mar 2017 16:22:24 +0000 (+0000)
Subject: [SelectionDAG] Support BUILD_VECTOR implicit truncation in SelectionDAG::ComputeNumSi... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=a1d8ce502da4c015c44c4523ceb55ca551c554ed;p=llvm

[SelectionDAG] Support BUILD_VECTOR implicit truncation in SelectionDAG::ComputeNumSignBits (PR32273)

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@297852 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 85747ac623b..026572222ea 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -2906,9 +2906,20 @@ unsigned SelectionDAG::ComputeNumSignBits(SDValue Op, unsigned Depth) const {
   }
 
   case ISD::BUILD_VECTOR:
-    Tmp = ComputeNumSignBits(Op.getOperand(0), Depth + 1);
-    for (unsigned i = 1, e = Op.getNumOperands(); (i < e) && (Tmp > 1); ++i)
-      Tmp = std::min(Tmp, ComputeNumSignBits(Op.getOperand(i), Depth + 1));
+    Tmp = VTBits;
+    for (unsigned i = 0, e = Op.getNumOperands(); (i < e) && (Tmp > 1); ++i) {
+      SDValue SrcOp = Op.getOperand(i);
+      Tmp2 = ComputeNumSignBits(Op.getOperand(i), Depth + 1);
+
+      // BUILD_VECTOR can implicitly truncate sources, we must handle this.
+      if (SrcOp.getValueSizeInBits() != VTBits) {
+        assert(SrcOp.getValueSizeInBits() > VTBits &&
+               "Expected BUILD_VECTOR implicit truncation");
+        unsigned ExtraBits = SrcOp.getValueSizeInBits() - VTBits;
+        Tmp2 = (Tmp2 > ExtraBits ? Tmp2 - ExtraBits : 1);
+      }
+      Tmp = std::min(Tmp, Tmp2);
+    }
     return Tmp;
 
   case ISD::SIGN_EXTEND:
diff --git a/test/CodeGen/AArch64/dag-numsignbits.ll b/test/CodeGen/AArch64/dag-numsignbits.ll
index 246d0e6f2b8..217c3df77c9 100644
--- a/test/CodeGen/AArch64/dag-numsignbits.ll
+++ b/test/CodeGen/AArch64/dag-numsignbits.ll
@@ -6,10 +6,10 @@ define void @signbits_vXi1(<4 x i16> %a1) {
 ; CHECK-LABEL: signbits_vXi1
 ; CHECK: cmgt v0.4h, v1.4h, v0.4h
 ; CHECK-NEXT: and v0.8b, v0.8b, v2.8b
-; CHECK-NEXT: umov w8, v0.h[0]
-; CHECK-NEXT: umov w9, v0.h[3]
-; CHECK-NEXT: and w0, w8, #0x1
-; CHECK-NEXT: and w3, w9, #0x1
+; CHECK-NEXT: shl v0.4h, v0.4h, #15
+; CHECK-NEXT: sshr v0.4h, v0.4h, #15
+; CHECK-NEXT: umov w0, v0.h[0]
+; CHECK-NEXT: umov w3, v0.h[3]
 ; CHECK-NEXT: mov w1, wzr
 ; CHECK-NEXT: mov w2, wzr
 ; CHECK-NEXT: b foo