Revert "Revert "[ConstHoist] Do not rebase single (or few) dependent constant""

This reverts commit bd7b44f35ee9fbe365eb25ce55437ea793b39346.

Reland r342994: disabled the optimization and explicitly enable it in test.

-mllvm -consthoist-min-num-to-rebase<unsigned>=0

[ConstHoist] Do not rebase single (or few) dependent constant

If an instance (InsertionPoint or IP) of Base constant A has only one or few
rebased constants depending on it, do NOT rebase. One extra ADD instruction is
required to materialize each rebased constant, assuming A and the rebased have
the same materialization cost.

Differential Revision: https://reviews.llvm.org/D52243

llvm-svn: 343053

1 files changed, 191 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/Thumb/consthoist-few-dependents.ll b/llvm/test/CodeGen/Thumb/consthoist-few-dependents.ll
new file mode 100644
index 00000000000..4141cf38a93
--- /dev/null
+++ b/llvm/test/CodeGen/Thumb/consthoist-few-dependents.ll
@@ -0,0 +1,191 @@
+; RUN: opt -consthoist -S %s -o - | FileCheck %s --check-prefix=OPT
+; RUN: opt -consthoist -S -consthoist-min-num-to-rebase=1 %s -o - | FileCheck %s --check-prefix=OPT --check-prefix=OPT-1
+; RUN: opt -consthoist -S -consthoist-min-num-to-rebase=2 %s -o - | FileCheck %s --check-prefix=OPT --check-prefix=OPT-2
+; RUN: opt -consthoist -S -consthoist-min-num-to-rebase=3 %s -o - | FileCheck %s --check-prefix=OPT --check-prefix=OPT-3
+
+; RUN: llc -consthoist-min-num-to-rebase=2 %s -o - | FileCheck %s --check-prefix=LLC
+
+target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv6m-none-unknown-musleabi"
+
+; Test that constant 0 and 1 of i1 type is NOT hoisted due low
+; materializing cost.
+
+; OPT-LABEL: avalon
+; OPT: bb1:
+; OPT: store i1 true
+; OPT: bb2:
+; OPT: store i1 false
+; OPT: bb3:
+; OPT: store i1 false
+; OPT: store i1 false
+; OPT-NOT: add
+
+; LLC-LABEL: avalon
+; LLC-DAG: movs r{{[0-9]+}}, #0
+; LLC-DAG: movs r{{[0-9]+}}, #0
+; LLC-DAG: movs r{{[0-9]+}}, #1
+; LLC-NOT: add
+
+@global = local_unnamed_addr global i1 undef, align 1
+@global.0 = local_unnamed_addr global i1 undef, align 1
+
+define void @avalon() #0 {
+bb:
+  switch i8 undef, label %bb5 [
+    i8 0, label %bb1
+    i8 -1, label %bb2
+    i8 1, label %bb3
+  ]
+
+bb1:
+  store i1 1, i1* @global, align 1
+  unreachable
+
+bb2:
+  store i1 0, i1* @global, align 1
+  unreachable
+
+bb3:
+  store i1 0, i1* @global.0, align 1
+  store i1 0, i1* @global, align 1
+  unreachable
+
+bb5:
+  ret void
+}
+
+; Test that for i8 type, constant -1 is not rebased since it's the only
+; dependent of base constant -2.
+; This test is also covered by r342898, see
+; test/CodeGen/Thumb/consthoist-imm8-costs-1.ll
+
+; OPT-2-LABEL: barney
+; OPT-2: bb1:
+; OPT-2: store i8 -1
+; OPT-2: bb2:
+; OPT-2: store i8 -2
+; OPT-2: bb3:
+; OPT-2: store i8 -2
+; OPT-2: store i8 -2
+; OPT-2-NOT: add
+
+; LLC-LABEL: barney
+; LLC-DAG: movs r{{[0-9]+}}, #254
+; LLC-DAG: movs r{{[0-9]+}}, #255
+; LLC-NOT: mvn
+; LLC-NOT: add
+
+@global.1 = local_unnamed_addr global i8 undef, align 1
+@global.2 = local_unnamed_addr global i8 undef, align 1
+
+define void @barney() #0 {
+bb:
+  switch i8 undef, label %bb5 [
+    i8 0, label %bb1
+    i8 -1, label %bb2
+    i8 1, label %bb3
+  ]
+
+bb1:                                              ; preds = %bb
+  store i8 -1, i8* @global.1, align 1
+  unreachable
+
+bb2:                                              ; preds = %bb
+  store i8 -2, i8* @global.1, align 1
+  unreachable
+
+bb3:                                              ; preds = %bb
+  store i8 -2, i8* @global.2, align 1
+  store i8 -2, i8* @global.1, align 1
+  unreachable
+
+bb5:                                              ; preds = %bb
+  ret void
+}
+
+; Test that for i16 type constant 65532 is not rebased if it's the only
+; dependent of base constant 65531. Cost would be the same if rebased.
+; If rebased, 3 two-byte instructions:
+;   movs    r0, #4
+;   mvns    r0, r0
+;   adds    r0, r0, #1
+; If NOT rebased, 1 two-byte instruction plus 1 four-byte CP entry:
+;           ldr     r1, .LCPI2_3
+;           ...
+;   .LCPI2_3:
+;           .long   65532
+
+; OPT-LABEL: carla
+
+; -consthoist-min-num-to-rebase=1, check that 65532 and single use of 65531
+; in bb2 is rebased
+; OPT-1: bb1:
+; OPT-1: %[[C1:const[0-9]?]] = bitcast i16 -5 to i16
+; OPT-1-NEXT: %const_mat = add i16 %[[C1]], 1
+; OPT-1-NEXT: store i16 %const_mat, i16* @global.3, align 1
+; OPT-1: bb2:
+; OPT-1-NEXT: %[[C2:const[0-9]?]] = bitcast i16 -5 to i16
+; OPT-1-NEXT: store i16 %[[C2]], i16* @global.3, align 1
+; OPT-1: bb3:
+; OPT-1-NEXT: %[[C3:const[0-9]?]] = bitcast i16 -5 to i16
+; OPT-1-NEXT: store i16 %[[C3]], i16* @global.4, align 1
+; OPT-1-NEXT: store i16 %[[C3]], i16* @global.3, align 1
+
+; -consthoist-min-num-to-rebase=2, check that 65532 and single use of 65531
+; in bb2 is not rebased
+; OPT-2: bb1:
+; OPT-2-NEXT: store i16 -4, i16* @global.3, align 1
+; OPT-2: bb2:
+; OPT-2-NEXT: store i16 -5, i16* @global.3, align 1
+; OPT-2: bb3:
+; OPT-2-NEXT:   %[[C4:const[0-9]?]] = bitcast i16 -5 to i16
+; OPT-2-NEXT:   store i16 %[[C4]], i16* @global.4, align 1
+; OPT-2-NEXT:   store i16 %[[C4]], i16* @global.3, align 1
+; OPT-2-NOT: add
+
+; -consthoist-min-num-to-rebase=3, check that dual uses of 65531 in bb3 are
+; not rebase
+; OPT-3: bb1:
+; OPT-3-NEXT: store i16 -4, i16* @global.3, align 1
+; OPT-3: bb2:
+; OPT-3-NEXT: store i16 -5, i16* @global.3, align 1
+; OPT-3: bb3:
+; OPT-3-NEXT:   store i16 -5, i16* @global.4, align 1
+; OPT-3-NEXT:   store i16 -5, i16* @global.3, align 1
+; OPT-3-NOT: add
+; OPT-3-NOT: bitcast
+
+; LLC-LABEL: carla
+; LLC-DAG: ldr r{{[0-9]+}}, .LCPI2_1
+; LLC-DAG: ldr r{{[0-9]+}}, .LCPI2_3
+; LLC-NOT: mvn
+; LLC-NOT: add
+
+@global.3 = local_unnamed_addr global i16 undef, align 2
+@global.4 = local_unnamed_addr global i16 undef, align 2
+
+define void @carla() {
+bb:
+  switch i8 undef, label %bb5 [
+    i8 0, label %bb1
+    i8 -1, label %bb2
+    i8 1, label %bb3
+  ]
+
+bb1:                                              ; preds = %bb
+  store i16 65532, i16* @global.3, align 1
+  unreachable
+
+bb2:                                              ; preds = %bb
+  store i16 65531, i16* @global.3, align 1
+  unreachable
+
+bb3:                                              ; preds = %bb
+  store i16 65531, i16* @global.4, align 1
+  store i16 65531, i16* @global.3, align 1
+  unreachable
+
+bb5:                                              ; preds = %bb
+  ret void
+}