[SeparateConstOffsetFromGEP] Preserve inbounds flag based on ValueTracking

If we know that the initial GEP was inbounds, and we change it to a
sequence of GEPs from the same base pointer where every offset is
non-negative, then the new GEPs are inbounds.

For SWDEV-516125.

Author: ritter-x2a

Diff for: llvm/lib/Transforms/Scalar/SeparateConstOffsetFromGEP.cpp

@@ -1052,6 +1052,8 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
     }
   }
 
+  bool MayRecoverInbounds = AccumulativeByteOffset >= 0 && GEP->isInBounds();
+
   // Remove the constant offset in each sequential index. The resultant GEP
   // computes the variadic base.
   // Notice that we don't remove struct field indices here. If LowerGEP is
@@ -1079,6 +1081,8 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
         // and the old index if they are not used.
         RecursivelyDeleteTriviallyDeadInstructions(UserChainTail);
         RecursivelyDeleteTriviallyDeadInstructions(OldIdx);
+        MayRecoverInbounds =
+            MayRecoverInbounds && computeKnownBits(NewIdx, *DL).isNonNegative();
       }
     }
   }
@@ -1100,11 +1104,15 @@ bool SeparateConstOffsetFromGEP::splitGEP(GetElementPtrInst *GEP) {
   // address with silently-wrapping two's complement arithmetic".
   // Therefore, the final code will be a semantically equivalent.
   //
-  // TODO(jingyue): do some range analysis to keep as many inbounds as
-  // possible. GEPs with inbounds are more friendly to alias analysis.
-  // TODO(gep_nowrap): Preserve nuw at least.
-  GEPNoWrapFlags NewGEPFlags = GEPNoWrapFlags::none();
-  GEP->setNoWrapFlags(GEPNoWrapFlags::none());
+  // If the initial GEP was inbounds and all variable indices and the
+  // accumulated offsets are non-negative, they can be added in any order and
+  // the intermediate results are in bounds. So, we can preserve the inbounds
+  // flag for both GEPs. GEPs with inbounds are more friendly to alias analysis.
+  //
+  // TODO(gep_nowrap): Preserve nuw?
+  GEPNoWrapFlags NewGEPFlags =
+      MayRecoverInbounds ? GEPNoWrapFlags::inBounds() : GEPNoWrapFlags::none();
+  GEP->setNoWrapFlags(NewGEPFlags);
 
   // Lowers a GEP to either GEPs with a single index or arithmetic operations.
   if (LowerGEP) {

Diff for: llvm/test/Transforms/SeparateConstOffsetFromGEP/AMDGPU/preserve-inbounds.ll

@@ -16,3 +16,26 @@ entry:
   %arrayidx = getelementptr inbounds i32, ptr %p, i64 %idx
   ret ptr %arrayidx
 }
+
+; All offsets must be positive, so inbounds can be preserved.
+define void @must_be_inbounds(ptr %dst, ptr %src, i32 %i) {
+; CHECK-LABEL: @must_be_inbounds(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[I_PROM:%.*]] = zext i32 [[I:%.*]] to i64
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds float, ptr [[SRC:%.*]], i64 [[I_PROM]]
+; CHECK-NEXT:    [[ARRAYIDX_SRC2:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 4
+; CHECK-NEXT:    [[TMP1:%.*]] = load float, ptr [[ARRAYIDX_SRC2]], align 4
+; CHECK-NEXT:    [[TMP2:%.*]] = getelementptr inbounds float, ptr [[DST:%.*]], i64 [[I_PROM]]
+; CHECK-NEXT:    [[ARRAYIDX_DST4:%.*]] = getelementptr inbounds i8, ptr [[TMP2]], i64 4
+; CHECK-NEXT:    store float [[TMP1]], ptr [[ARRAYIDX_DST4]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %i.prom = zext i32 %i to i64
+  %idx = add nsw i64 %i.prom, 1
+  %arrayidx.src = getelementptr inbounds float, ptr %src, i64 %idx
+  %3 = load float, ptr %arrayidx.src, align 4
+  %arrayidx.dst = getelementptr inbounds float, ptr %dst, i64 %idx
+  store float %3, ptr %arrayidx.dst, align 4
+  ret void
+}

Diff for: llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep-and-gvn.ll

@@ -157,19 +157,19 @@ define void @sum_of_array3(i32 %x, i32 %y, ptr nocapture %output) {
 ; IR-NEXT:  .preheader:
 ; IR-NEXT:    [[TMP0:%.*]] = zext i32 [[Y]] to i64
 ; IR-NEXT:    [[TMP1:%.*]] = zext i32 [[X]] to i64
-; IR-NEXT:    [[TMP2:%.*]] = getelementptr [32 x [32 x float]], ptr addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
+; IR-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [32 x [32 x float]], ptr addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
 ; IR-NEXT:    [[TMP3:%.*]] = addrspacecast ptr addrspace(3) [[TMP2]] to ptr
 ; IR-NEXT:    [[TMP4:%.*]] = load float, ptr [[TMP3]], align 4
 ; IR-NEXT:    [[TMP5:%.*]] = fadd float [[TMP4]], 0.000000e+00
-; IR-NEXT:    [[TMP6:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 4
+; IR-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 4
 ; IR-NEXT:    [[TMP7:%.*]] = addrspacecast ptr addrspace(3) [[TMP6]] to ptr
 ; IR-NEXT:    [[TMP8:%.*]] = load float, ptr [[TMP7]], align 4
 ; IR-NEXT:    [[TMP9:%.*]] = fadd float [[TMP5]], [[TMP8]]
-; IR-NEXT:    [[TMP10:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 128
+; IR-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 128
 ; IR-NEXT:    [[TMP11:%.*]] = addrspacecast ptr addrspace(3) [[TMP10]] to ptr
 ; IR-NEXT:    [[TMP12:%.*]] = load float, ptr [[TMP11]], align 4
 ; IR-NEXT:    [[TMP13:%.*]] = fadd float [[TMP9]], [[TMP12]]
-; IR-NEXT:    [[TMP14:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 132
+; IR-NEXT:    [[TMP14:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 132
 ; IR-NEXT:    [[TMP15:%.*]] = addrspacecast ptr addrspace(3) [[TMP14]] to ptr
 ; IR-NEXT:    [[TMP16:%.*]] = load float, ptr [[TMP15]], align 4
 ; IR-NEXT:    [[TMP17:%.*]] = fadd float [[TMP13]], [[TMP16]]
@@ -224,19 +224,19 @@ define void @sum_of_array4(i32 %x, i32 %y, ptr nocapture %output) {
 ; IR-NEXT:  .preheader:
 ; IR-NEXT:    [[TMP0:%.*]] = zext i32 [[Y]] to i64
 ; IR-NEXT:    [[TMP1:%.*]] = zext i32 [[X]] to i64
-; IR-NEXT:    [[TMP2:%.*]] = getelementptr [32 x [32 x float]], ptr addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
+; IR-NEXT:    [[TMP2:%.*]] = getelementptr inbounds [32 x [32 x float]], ptr addrspace(3) @array, i64 0, i64 [[TMP1]], i64 [[TMP0]]
 ; IR-NEXT:    [[TMP3:%.*]] = addrspacecast ptr addrspace(3) [[TMP2]] to ptr
 ; IR-NEXT:    [[TMP4:%.*]] = load float, ptr [[TMP3]], align 4
 ; IR-NEXT:    [[TMP5:%.*]] = fadd float [[TMP4]], 0.000000e+00
-; IR-NEXT:    [[TMP6:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 4
+; IR-NEXT:    [[TMP6:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 4
 ; IR-NEXT:    [[TMP7:%.*]] = addrspacecast ptr addrspace(3) [[TMP6]] to ptr
 ; IR-NEXT:    [[TMP8:%.*]] = load float, ptr [[TMP7]], align 4
 ; IR-NEXT:    [[TMP9:%.*]] = fadd float [[TMP5]], [[TMP8]]
-; IR-NEXT:    [[TMP10:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 128
+; IR-NEXT:    [[TMP10:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 128
 ; IR-NEXT:    [[TMP11:%.*]] = addrspacecast ptr addrspace(3) [[TMP10]] to ptr
 ; IR-NEXT:    [[TMP12:%.*]] = load float, ptr [[TMP11]], align 4
 ; IR-NEXT:    [[TMP13:%.*]] = fadd float [[TMP9]], [[TMP12]]
-; IR-NEXT:    [[TMP14:%.*]] = getelementptr i8, ptr addrspace(3) [[TMP2]], i64 132
+; IR-NEXT:    [[TMP14:%.*]] = getelementptr inbounds i8, ptr addrspace(3) [[TMP2]], i64 132
 ; IR-NEXT:    [[TMP15:%.*]] = addrspacecast ptr addrspace(3) [[TMP14]] to ptr
 ; IR-NEXT:    [[TMP16:%.*]] = load float, ptr [[TMP15]], align 4
 ; IR-NEXT:    [[TMP17:%.*]] = fadd float [[TMP13]], [[TMP16]]

Diff for: llvm/test/Transforms/SeparateConstOffsetFromGEP/NVPTX/split-gep.ll

@@ -372,8 +372,8 @@ define ptr @trunk_explicit(ptr %ptr, i64 %idx) {
 ; CHECK-LABEL: define ptr @trunk_explicit(
 ; CHECK-SAME: ptr [[PTR:%.*]], i64 [[IDX:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
-; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr i8, ptr [[TMP0]], i64 3216
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
+; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 3216
 ; CHECK-NEXT:    ret ptr [[PTR21]]
 ;
 entry:
@@ -389,8 +389,8 @@ define ptr @trunk_long_idx(ptr %ptr, i64 %idx) {
 ; CHECK-LABEL: define ptr @trunk_long_idx(
 ; CHECK-SAME: ptr [[PTR:%.*]], i64 [[IDX:%.*]]) {
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
-; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr i8, ptr [[TMP0]], i64 3216
+; CHECK-NEXT:    [[TMP0:%.*]] = getelementptr inbounds [[STRUCT0:%.*]], ptr [[PTR]], i64 0, i32 3, i64 [[IDX]], i32 1
+; CHECK-NEXT:    [[PTR21:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 3216
 ; CHECK-NEXT:    ret ptr [[PTR21]]
 ;
 entry: