Index: lib/Analysis/InstructionSimplify.cpp
===================================================================
--- lib/Analysis/InstructionSimplify.cpp
+++ lib/Analysis/InstructionSimplify.cpp
@@ -4940,7 +4940,15 @@
   case Intrinsic::log2:
     // log2(exp2(x)) -> x
     if (Q.CxtI->hasAllowReassoc() &&
-        match(Op0, m_Intrinsic<Intrinsic::exp2>(m_Value(X)))) return X;
+        (match(Op0, m_Intrinsic<Intrinsic::exp2>(m_Value(X))) ||
+         match(Op0, m_Intrinsic<Intrinsic::pow>(m_SpecificFP(2.0),
+                                                m_Value(X))))) return X;
+    break;
+  case Intrinsic::log10:
+    // log10(pow(10.0, x)) -> x
+    if (Q.CxtI->hasAllowReassoc() &&
+        match(Op0, m_Intrinsic<Intrinsic::pow>(m_SpecificFP(10.0),
+                                               m_Value(X)))) return X;
     break;
   default:
     break;
Index: test/Transforms/InstSimplify/log10-pow10-intrinsic.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstSimplify/log10-pow10-intrinsic.ll
@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instsimplify < %s | FileCheck %s
+
+declare double @llvm.log10.f64(double)
+declare double @llvm.pow.f64(double, double)
+
+define double @log10_pow10(double %x) {
+; CHECK-LABEL: @log10_pow10(
+; CHECK-NEXT:    [[TMP1:%.*]] = call double @llvm.pow.f64(double 1.000000e+01, double [[X:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call double @llvm.log10.f64(double [[TMP1]])
+; CHECK-NEXT:    ret double [[TMP2]]
+;
+  %1 = call double @llvm.pow.f64(double 10.000000e+00, double %x)
+  %2 = call double @llvm.log10.f64(double %1)
+  ret double %2
+}
+
+define double @log10_strict_pow10_reassoc(double %x) {
+; CHECK-LABEL: @log10_strict_pow10_reassoc(
+; CHECK-NEXT:    [[TMP1:%.*]] = call reassoc double @llvm.pow.f64(double 1.000000e+01, double [[X:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call double @llvm.log10.f64(double [[TMP1]])
+; CHECK-NEXT:    ret double [[TMP2]]
+;
+  %1 = call reassoc double @llvm.pow.f64(double 10.000000e+00, double %x)
+  %2 = call double @llvm.log10.f64(double %1)
+  ret double %2
+}
+
+define double @log10_reassoc_pow10_strict(double %x) {
+; CHECK-LABEL: @log10_reassoc_pow10_strict(
+; CHECK-NEXT:    ret double [[X:%.*]]
+;
+  %1 = call double @llvm.pow.f64(double 10.000000e+00, double %x)
+  %2 = call reassoc double @llvm.log10.f64(double %1)
+  ret double %2
+}
+
+define double @log10_pow10_reassoc(double %x) {
+; CHECK-LABEL: @log10_pow10_reassoc(
+; CHECK-NEXT:    ret double [[X:%.*]]
+;
+  %1 = call reassoc double @llvm.pow.f64(double 10.000000e+00, double %x)
+  %2 = call reassoc double @llvm.log10.f64(double %1)
+  ret double %2
+}
Index: test/Transforms/InstSimplify/log2-pow2-intrinsic.ll
===================================================================
--- /dev/null
+++ test/Transforms/InstSimplify/log2-pow2-intrinsic.ll
@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -instsimplify < %s | FileCheck %s
+
+declare double @llvm.log2.f64(double)
+declare double @llvm.pow.f64(double, double)
+
+define double @log2_pow2(double %x) {
+; CHECK-LABEL: @log2_pow2(
+; CHECK-NEXT:    [[TMP1:%.*]] = call double @llvm.pow.f64(double 2.000000e+00, double [[X:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call double @llvm.log2.f64(double [[TMP1]])
+; CHECK-NEXT:    ret double [[TMP2]]
+;
+  %1 = call double @llvm.pow.f64(double 2.000000e+00, double %x)
+  %2 = call double @llvm.log2.f64(double %1)
+  ret double %2
+}
+
+define double @log2_strict_pow2_reassoc(double %x) {
+; CHECK-LABEL: @log2_strict_pow2_reassoc(
+; CHECK-NEXT:    [[TMP1:%.*]] = call reassoc double @llvm.pow.f64(double 2.000000e+00, double [[X:%.*]])
+; CHECK-NEXT:    [[TMP2:%.*]] = call double @llvm.log2.f64(double [[TMP1]])
+; CHECK-NEXT:    ret double [[TMP2]]
+;
+  %1 = call reassoc double @llvm.pow.f64(double 2.000000e+00, double %x)
+  %2 = call double @llvm.log2.f64(double %1)
+  ret double %2
+}
+
+define double @log2_reassoc_pow2_strict(double %x) {
+; CHECK-LABEL: @log2_reassoc_pow2_strict(
+; CHECK-NEXT:    ret double [[X:%.*]]
+;
+  %1 = call double @llvm.pow.f64(double 2.000000e+00, double %x)
+  %2 = call reassoc double @llvm.log2.f64(double %1)
+  ret double %2
+}
+
+define double @log2_pow2_reassoc(double %x) {
+; CHECK-LABEL: @log2_pow2_reassoc(
+; CHECK-NEXT:    ret double [[X:%.*]]
+;
+  %1 = call reassoc double @llvm.pow.f64(double 2.000000e+00, double %x)
+  %2 = call reassoc double @llvm.log2.f64(double %1)
+  ret double %2
+}