[llvm] Reland "[InstructionSimplify] Enhance simplifySelectInst() (#163453)" (PR #164694)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,280 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt < %s -S -passes=instcombine | FileCheck %s
+ at A = extern_weak global float, align 4
+
+; %same.as.v1 is a select with two phis %v1 and %phi.to.remove as the true
+; and false values, while %v1 and %phi.to.remove are actually the same.
+; Fold the selection instruction %same.as.v1 to %v1.
+define void @select_with_identical_phi(ptr %m, ptr %n, i32 %count) {
+; CHECK-LABEL: @select_with_identical_phi(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.body:
+; CHECK-NEXT:    [[V0:%.*]] = phi float [ 0x4415AF1D80000000, [[ENTRY:%.*]] ], [ [[V0_1:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[V1:%.*]] = phi float [ 0xC415AF1D80000000, [[ENTRY]] ], [ [[V1_1:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ 0, [[ENTRY]] ], [ [[INC_I:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[Q:%.*]] = phi ptr [ [[M:%.*]], [[ENTRY]] ], [ [[Q_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[C:%.*]] = phi ptr [ [[N:%.*]], [[ENTRY]] ], [ [[C_NEXT:%.*]], [[FOR_BODY]] ]
+; CHECK-NEXT:    [[Q_LOAD:%.*]] = load float, ptr [[Q]], align 4
+; CHECK-NEXT:    [[C_LOAD:%.*]] = load float, ptr [[C]], align 4
+; CHECK-NEXT:    [[SUB:%.*]] = fsub float [[Q_LOAD]], [[C_LOAD]]
+; CHECK-NEXT:    [[CMP1:%.*]] = fcmp olt float [[SUB]], [[V0]]
+; CHECK-NEXT:    [[V0_1]] = select i1 [[CMP1]], float [[SUB]], float [[V0]]
+; CHECK-NEXT:    [[CMP2:%.*]] = fcmp ogt float [[SUB]], [[V1]]
+; CHECK-NEXT:    [[V1_1]] = select i1 [[CMP2]], float [[SUB]], float [[V1]]
+; CHECK-NEXT:    [[INC_I]] = add nuw nsw i32 [[I]], 1
+; CHECK-NEXT:    [[Q_NEXT]] = getelementptr inbounds nuw i8, ptr [[Q]], i64 4
+; CHECK-NEXT:    [[C_NEXT]] = getelementptr inbounds nuw i8, ptr [[C]], i64 4
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp eq i32 [[INC_I]], [[COUNT:%.*]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[EXIT:%.*]], label [[FOR_BODY]]
+; CHECK:       exit:
+; CHECK-NEXT:    store float [[V1_1]], ptr @A, align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  br label %for.body
+
+for.body:                                    ; preds = %entry, %for.body
+  %v0 = phi float [ 0x4415AF1D80000000, %entry ], [ %v0.1, %for.body ]
+  %v1 = phi float [ 0xC415AF1D80000000, %entry ], [ %v1.1, %for.body ]
+  %phi.to.remove = phi float [ 0xC415AF1D80000000, %entry ], [ %phi.to.remove.next, %for.body ]
+  %i = phi i32 [ 0, %entry ], [ %inc.i, %for.body ]
+  %q = phi ptr [ %m, %entry ], [ %q.next, %for.body ]
+  %c = phi ptr [ %n, %entry ], [ %c.next, %for.body ]
+  %q.load = load float, ptr %q
+  %c.load = load float, ptr %c
+  %sub = fsub float %q.load, %c.load
+  %cmp1 = fcmp olt float %sub, %v0
+  %v0.1 = select i1 %cmp1, float %sub, float %v0
+  %same.as.v1 = select i1 %cmp1, float %v1, float %phi.to.remove
+  %cmp2 = fcmp ogt float  %sub, %same.as.v1
+  %v1.1 = select i1 %cmp2, float %sub, float %v1
+  %phi.to.remove.next = select i1 %cmp2, float %sub, float %same.as.v1
+  %inc.i = add nuw nsw i32 %i, 1
+  %q.next = getelementptr inbounds i8, ptr %q, i64 4
+  %c.next = getelementptr inbounds i8, ptr %c, i64 4
+  %exitcond = icmp eq i32 %inc.i, %count
+  br i1 %exitcond, label %exit, label %for.body
+
+exit:
+  %vl.1.lcssa = phi float [ %v1.1, %for.body ]
+  store float %vl.1.lcssa, ptr @A
+  ret void
+}
+
+; Reduced from select_with_identical_phi().
+; Check that %same.as.v1 can be folded.
+define void @select_with_identical_phi_2(i1 %cmp1, i1 %cmp2, float %x) {
+; CHECK-LABEL: @select_with_identical_phi_2(
+; CHECK: select
+; CHECK-NOT: select
----------------
nikic wrote:

Please do keep the generated check lines.

https://github.com/llvm/llvm-project/pull/164694