[llvm] [InstCombine] Combine trunc (lshr X, BW-1) to i1 --> icmp slt X, 0 (#142593) (PR #143846)

[Simon Pilgrim via llvm-commits]

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@@ -815,6 +815,13 @@ Instruction *InstCombinerImpl::visitTrunc(TruncInst &Trunc) {
       return new ICmpInst(ICmpInst::ICMP_EQ, X, CmpC);
     }
 
+    if (match(Src, m_AShr(m_Value(X), m_SpecificInt(SrcWidth - 1))) ||
+        match(Src, m_LShr(m_Value(X), m_SpecificInt(SrcWidth - 1)))) {
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RKSimon wrote:

@mayanksolanki393 m_Shr will allow you to match both lshr/ashr in a single pattern

https://github.com/llvm/llvm-project/pull/143846