ConstRange: test edge-cases of makeAllowedICmpRegion (#127080)

Exhaustively test signed-unsigned min-max edge-cases of
makeAllowedICmpRegion.

Author: artagnon

llvm/unittests/IR/ConstantRangeTest.cpp

@@ -1631,11 +1631,35 @@ TEST_F(ConstantRangeTest, Ashr) {
             ConstantRange(APInt(16, 0xfffc), APInt(16, 0xfffe)));
 }
 
-TEST(ConstantRange, MakeAllowedICmpRegion) {
-  // PR8250
-  ConstantRange SMax = ConstantRange(APInt::getSignedMaxValue(32));
+TEST(ConstantRange, MakeAllowedICmpRegionEdgeCases) {
+  ConstantRange SMax = ConstantRange(APInt::getSignedMaxValue(8));
   EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SGT, SMax)
                   .isEmptySet());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SGE, SMax)
+                  .isSingleElement());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SLE, SMax)
+                  .isFullSet());
+  ConstantRange SMin = ConstantRange(APInt::getSignedMinValue(8));
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SLT, SMin)
+                  .isEmptySet());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SLE, SMin)
+                  .isSingleElement());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_SGE, SMin)
+                  .isFullSet());
+  ConstantRange UMax = ConstantRange(APInt::getMaxValue(8));
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_UGT, UMax)
+                  .isEmptySet());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_UGE, UMax)
+                  .isSingleElement());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_ULE, UMax)
+                  .isFullSet());
+  ConstantRange UMin = ConstantRange(APInt::getMinValue(8));
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_ULT, UMin)
+                  .isEmptySet());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_ULE, UMin)
+                  .isSingleElement());
+  EXPECT_TRUE(ConstantRange::makeAllowedICmpRegion(ICmpInst::ICMP_UGE, UMin)
+                  .isFullSet());
 }
 
 TEST(ConstantRange, MakeSatisfyingICmpRegion) {