[llvm] [InstCombine] Handle scalable splat in `getFlippedStrictnessPredicateAndConstant` (PR #83980)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/83980

This patch adds support for canonicalization of icmp with a scalable splat. Some optimizations assume that `icmp pred X, APInt C` is in canonical form.

Fixes https://github.com/llvm/llvm-project/issues/83947.

>From f41ad45565625d5dea68a2fad7979a350f818053 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 5 Mar 2024 17:21:16 +0800
Subject: [PATCH] [InstCombine] Handle scalable splat in
 `getFlippedStrictnessPredicateAndConstant`

---
 .../InstCombine/InstCombineCompares.cpp           |  7 +++++++
 llvm/test/Transforms/InstCombine/pr83931.ll       | 15 +++++++++++++++
 llvm/test/Transforms/InstCombine/select.ll        |  2 +-
 llvm/test/Transforms/InstCombine/vscale_cmp.ll    |  2 +-
 4 files changed, 24 insertions(+), 2 deletions(-)
 create mode 100644 llvm/test/Transforms/InstCombine/pr83931.ll

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 49e597171b1c6f..5026da6007d31d 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -6544,6 +6544,13 @@ InstCombiner::getFlippedStrictnessPredicateAndConstant(CmpInst::Predicate Pred,
       if (!SafeReplacementConstant)
         SafeReplacementConstant = CI;
     }
+  } else if (isa<VectorType>(C->getType())) {
+    // Handle scalable splat
+    Value *SplatC = C->getSplatValue();
+    auto *CI = dyn_cast_or_null<ConstantInt>(SplatC);
+    // Bail out if the constant can't be safely incremented/decremented.
+    if (!CI || !ConstantIsOk(CI))
+      return std::nullopt;
   } else {
     // ConstantExpr?
     return std::nullopt;
diff --git a/llvm/test/Transforms/InstCombine/pr83931.ll b/llvm/test/Transforms/InstCombine/pr83931.ll
new file mode 100644
index 00000000000000..d36ac8d91abd30
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pr83931.ll
@@ -0,0 +1,15 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+define <vscale x 2 x i1> @dont_crash(<vscale x 2 x i64> %x) {
+; CHECK-LABEL: define <vscale x 2 x i1> @dont_crash(
+; CHECK-SAME: <vscale x 2 x i64> [[X:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[RET:%.*]] = icmp sgt <vscale x 2 x i64> [[X]], shufflevector (<vscale x 2 x i64> insertelement (<vscale x 2 x i64> poison, i64 -309383, i64 0), <vscale x 2 x i64> poison, <vscale x 2 x i32> zeroinitializer)
+; CHECK-NEXT:    ret <vscale x 2 x i1> [[RET]]
+;
+entry:
+  %div = sdiv <vscale x 2 x i64> %x, splat (i64 309383)
+  %ret = icmp sge <vscale x 2 x i64> %div, zeroinitializer
+  ret <vscale x 2 x i1> %ret
+}
diff --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 82baf05977dbb0..4676129e3a1cd6 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -3423,7 +3423,7 @@ define <vscale x 2 x i32> @scalable_sign_bits(<vscale x 2 x i8> %x) {
 define <vscale x 2 x i1> @scalable_non_zero(<vscale x 2 x i32> %x) {
 ; CHECK-LABEL: @scalable_non_zero(
 ; CHECK-NEXT:    [[A:%.*]] = or <vscale x 2 x i32> [[X:%.*]], shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> poison, i32 1, i64 0), <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ule <vscale x 2 x i32> [[A]], shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> poison, i32 56, i64 0), <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer)
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <vscale x 2 x i32> [[A]], shufflevector (<vscale x 2 x i32> insertelement (<vscale x 2 x i32> poison, i32 57, i64 0), <vscale x 2 x i32> poison, <vscale x 2 x i32> zeroinitializer)
 ; CHECK-NEXT:    ret <vscale x 2 x i1> [[CMP]]
 ;
   %a = or <vscale x 2 x i32> %x, splat (i32 1)
diff --git a/llvm/test/Transforms/InstCombine/vscale_cmp.ll b/llvm/test/Transforms/InstCombine/vscale_cmp.ll
index a7f8368c5d62c8..b2bfc93da089fc 100644
--- a/llvm/test/Transforms/InstCombine/vscale_cmp.ll
+++ b/llvm/test/Transforms/InstCombine/vscale_cmp.ll
@@ -3,7 +3,7 @@
 
 define <vscale x 2 x i1> @sge(<vscale x 2 x i8> %x) {
 ; CHECK-LABEL: @sge(
-; CHECK-NEXT:    [[CMP:%.*]] = icmp sge <vscale x 2 x i8> [[X:%.*]], zeroinitializer
+; CHECK-NEXT:    [[CMP:%.*]] = icmp sgt <vscale x 2 x i8> [[X:%.*]], shufflevector (<vscale x 2 x i8> insertelement (<vscale x 2 x i8> poison, i8 -1, i64 0), <vscale x 2 x i8> poison, <vscale x 2 x i32> zeroinitializer)
 ; CHECK-NEXT:    ret <vscale x 2 x i1> [[CMP]]
 ;
   %cmp = icmp sge <vscale x 2 x i8> %x, zeroinitializer