[llvm] [X86] Fold some (truncate (srl (add X, C1), C2)) patterns to (add (truncate (srl X, C2)), C1') (PR #126448)

[João Gouveia via llvm-commits]

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@@ -0,0 +1,138 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=x86_64-unknown | FileCheck %s --check-prefixes=X64
+
+; Test for https://github.com/llvm/llvm-project/issues/123239
+
+define i1 @test_ult_trunc_add(i64 %x) {
+; X64-LABEL: test_ult_trunc_add:
+; X64:       # %bb.0: # %entry
+; X64-NEXT:    shrq $48, %rdi
+; X64-NEXT:    addl $-65522, %edi # imm = 0xFFFF000E
+; X64-NEXT:    movzwl %di, %eax
+; X64-NEXT:    cmpl $3, %eax
+; X64-NEXT:    setb %al
+; X64-NEXT:    retq
+entry:
+  %add = add i64 %x, 3940649673949184
+  %shr = lshr i64 %add, 48
+  %conv = trunc i64 %shr to i32
+  %res = icmp ult i32 %conv, 3
+  ret i1 %res
+}
+
+define i1 @test_ult_add(i64 %x) {
+; X64-LABEL: test_ult_add:
+; X64:       # %bb.0: # %entry
+; X64-NEXT:    shrq $48, %rdi
+; X64-NEXT:    addl $-65522, %edi # imm = 0xFFFF000E
+; X64-NEXT:    movzwl %di, %eax
+; X64-NEXT:    cmpl $3, %eax
+; X64-NEXT:    setb %al
+; X64-NEXT:    retq
+entry:
+    %0 = add i64 3940649673949184, %x
+    %1 = icmp ult i64 %0, 844424930131968
+    ret i1 %1
+}
+
+define i1 @test_ugt_trunc_add(i64 %x) {
+; X64-LABEL: test_ugt_trunc_add:
+; X64:       # %bb.0: # %entry
+; X64-NEXT:    shrq $48, %rdi
+; X64-NEXT:    addl $-65522, %edi # imm = 0xFFFF000E
+; X64-NEXT:    movzwl %di, %eax
+; X64-NEXT:    cmpl $4, %eax
+; X64-NEXT:    setae %al
+; X64-NEXT:    retq
+entry:
+  %add = add i64 %x, 3940649673949184
+  %shr = lshr i64 %add, 48
+  %conv = trunc i64 %shr to i32
+  %res = icmp ugt i32 %conv, 3
+  ret i1 %res
+}
+
+define i1 @test_ugt_add(i64 %x) {
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joaotgouveia wrote:

No, this transformation is also applicable to those tests. However, the selection DAG differs in those cases, so I figured expanding the transformation to include them should be a separate patch. If preferred, I can expand it now, though.

https://github.com/llvm/llvm-project/pull/126448